Forum on Carbon Neutrality and Sustainable Environment

Keywords: energy storage, net-zero, electricity sector, batteries, thermal storage

A central strategy for achieving global, net zero economy wide emissions is decar¬¬bon¬¬izing the electricity sector while using this decarbonized electricity to electrify as much of the rest of the economy as possible. Electricity sector decarbonization has focused on replacing fossil fueled generation with variable renewable energy (VRE) generation, pri¬marily solar and wind. At small penetration of VRE’s, incorporation of these resources into the electricity system is fairly straightforward. However, as electricity systems around the world deploy significant amounts of VRE’s, it is impossible to match electricity supply and demand without incorporating energy storage into the system. This presentation examines the role that grid-scale storage used as electricity-to-storage-to-electricity can play in deeply decarbonized electricity systems We look at technology options, system design incorporating storage, and policy/regulatory changes that may be needed to facilitate these future systems. The results presented here are based on the recent Future of Energy Storage study ^[1].

Four categories of grid-scale energy storage are considered: electrochemical, mechanical, thermal, and chemical. Among electrochemical technologies, we focus on three: lithium-ion batteries (the incumbent technology), redox flow batteries, and metal-air chemistries. Mechanical storage examines pumped hydro-storage and compressed air energy storage. Thermal storage includes sensible heat storage in very low-cost materials, e.g., molten salts and rocks, as well as heat pumps. Finally chemical storage is illustrated with hydrogen, which if not ultimately used would certainly be a precursor to candidate storage chemicals. Operating characteristics and cost estimates projected out to 2050 are developed for each one of these technologies. All technologies studied are TRL level 6 or higher.

A capacity expansion model (GenX) is used to build out least cost electricity systems in different regions around the US as well as in India and Nigeria. In this way we are able to see how regional resources, weather patterns, and types of loads affect choice of over¬build-ing renewables, adding transmission, adding storage (of different types), and shifting de-mands.

Finally, policy and regulatory issues for these highly decarbonized electricity systems are discussed for several regions in the US. Specific policy and regulatory changes will certainly be affected by market structures and public attitudes among other factors in dif-ferent parts of the world.

References
[1] – The Future of Energy Storage, An Interdisciplinary MIT Study, https://energy.mit.edu/research/future-of-energy-storage/ (2022).

Lithium-ion batteries (LIBs) have dominated the market of portable electronics and electric vehicles due to their high energy density and long-term cyclability, and are moving forward to scale energy storage applications such as regulating the output of electricity generated by sustainable energy. Nevertheless, the current electrochemistry of LIBs based on Li-ion interaction/de-interaction between graphite anode and oxide cathode is suffering from intrinsic limitations of energy density, scarce natural resource (Li, Co, Ni etc.), and high energy consumption/CO₂ emission involved in the production of electrodes. Organic redox compounds, especially conjugated carbonyl compounds that have been studied since 1969, are reviving in the recent years due to the advantages of high capacity, abundant resources, and structural designability. Moreover, the electrochemical redox mechanism of organic carbonyl electrode materials mainly based on charge compensation enables the battery applications with versatile charge carriers (Li⁺, Na⁺, H⁺ etc.). The key challenges of organic carbonyl electrode materials are their high solubility in electrolyte during cycles and poor electronic conductivity, leading to fast capacity decay and inferior rate performance, respectively. This report focuses on the redox chemistry, structure-performance relationship, and applications of organic carbonyl electrode materials for Li and Na batteries. We developed several strategies from the aspects of molecular design (electrode level) and electrolyte optimization (electrolyte level) to solve the issues of organic carbonyl electrodes and construct high-performance Li/Na batteries. With elaborate design, organic carbonyl electrode materials have demonstrated promising interest for large-scale electrochemical energy storage in the foreseeable future.

Figure 1: Proposed strategies toward improving the electrochemical performance of organic carbonyl electrodes for Li/Na batteries.

References and selected publications
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[10] R. Shi, L. Liu, Y. Lu, C. Wang, Y. Li, L. Li, Z. Yan, J. Chen. Nature Commun. 2020, 11, 178.
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Electrical energy storage is becoming more and more important due to the widespread use of electrical vehicles and large-scale storage of electricity from wind farms and solar power plants for grid. Lithium ion batteries are taking a dominant role in these fields, and their consumption is exponentially increasing in recent years. However, the major elements of lithium, cobalt, nickel, etc used in lithium ion batteries are either rare or geographically unbalanced, mostly relying on import. Therefore, it is essential to find some alternative ways to replace lithium ion batteries or to recycle these substances greenly and efficiently. We have attempted in both ways in recent years. On the one hand, we have tried to explore resource-abundant dual-ion batteries and multiple ion batteries, and on the other hand, we have making efforts to directly recycle electrode materials from the spent lithium batteries in a green, cost-effective, and short-processing ways. In particular, we have obtained high-voltage cathode materials, regenerated graphite anode materials, and multi-functional high-performance electrocatalysts from the spent lithium ion batteries with good feasibility based on technical economic analysis.

This lecture will introduce what’s the meaning of net-zero carbon transformation for the global economy and how Stanford University organizes its energy ecosystem to help this transformation. Professor Cui will introduce his materials technology innovations for net-zero transformation and sustainability, including: 1) high energy battery technology for electrical transportation; 2) large scale energy storage technology for integrating solar and wind electricity into the grids; 3) air filtration technology for removal of PM2.5 and COVID viruses; 4) Warming and cooling textile technology for energy efficienncy; 5) Energy wall paper for building energy saving; 6) Water filtration technology to kill bacteria and viruses and to remove heavy metal; 7) Soil cleaning technology. He will also present his efforts on technology translation into the real world.

Sunlight-driven water splitting is studied actively for production of renewable solar hydrogen on a large scale. Overall water splitting using particulate photocatalysts has been attracting growing interest, because such systems can be spread over wide areas by inexpensive processes potentially. However, it is essential to radically improve the solar-to-hydrogen energy conversion efficiency (STH) of particulate photocatalysts and develop suitable reaction systems. In my talk, recent progress in photocatalytic materials and reaction systems will be presented.

The author’s group has studied various semiconductor oxides, (oxy)nitrides, and (oxy)chalcogenides as photocatalysts for water splitting. SrTiO₃ is an oxide photocatalyst that has been known to be active in overall water splitting under ultraviolet irradiation since 1980. Recently, the apparent quantum yield (AQY) of this photocatalyst in overall water splitting has been improved to more than 90% at 365 nm, equivalent to an internal quantum efficiency of almost unity, by refining the preparation conditions of the photocatalyst and the loading conditions of cocatalysts. This quantum efficiency is the highest yet reported and indicates that a particulate photocatalyst can drive the endergonic overall water splitting reaction at a quantum efficiency comparable to values obtained in photon-to-chemical and photon-to-current conversion processes by photosynthesis and photovoltaic systems, respectively. The author's group has also been developing panel reactors for large-scale applications. A solar hydrogen production system based on 100-m² arrayed photocatalytic water splitting panels and an oxyhydrogen gas-separation module was built, and its performance and system characteristics including safety issues were reported recently.

For practical solar energy harvesting, it is essential to develop photocatalysts that are active under visible light irradiation. Ta₃N₅ and Y₂Ti₂O₅S₂ photocatalysts are active in overall water splitting via one-step excitation under visible light irradiation. Particulate photocatalyst sheets efficiently split water into hydrogen and oxygen via two-step excitation, referred to as Z-scheme, regardless of the size. In particular, a photocatalyst sheet consisting of La- and Rh-codoped SrTiO₃ and Mo-doped BiVO₄ splits water into hydrogen and oxygen via the Z-scheme, showing a STH exceeding 1.0%. Some other (oxy)chalcogenides and (oxy)nitrides with long absorption edge wavelengths are also applicable to Z-scheme photocatalyst sheets and hold the promise of realizing greater STH values.

We live in the materials word. Materials defined the progress of humanity, as people moved from Stone Age to Bronze Age and then to Iron Age. Receiving access to new materials enabled new tools and technologies. We entered the Silicon Age more that half-a-century ago and, as a result, electronic and computer technologies greatly accelerated the technical progress, changing our life. What is next? Probably the Nanomaterials Age. The era of assembly of new materials, structures and devices from nanoscale building blocks providing any imaginable, but impossible in conventional materials, combinations of properties and functions. Assembly from nanoparticles will allow integration of electronics, energy harvesting and storage, creating self-powered internet of things and wearable internet. It may also minimize the waste during product manufacturing. 2D materials, like graphene, dozens of which are available nowadays and thousands more expected soon, provide very attractive building blocks, because they can easily assemble and self-assemble into dense structures, just like bricks in the wall.

There are currently many insulating and semiconducting 2D materials available, which can be used as single sheets in devices, or as building blocks. 2D transition metal carbides and nitrides (MXenes) have been expanding rapidly since their discovery at Drexel University in 2011. They added metallically conductive 2D building blocks to the available materials list. About 50 different MXenes have been synthesized, and the structure and properties of numerous other MXenes have been predicted using DFT calculations. Moreover, the availability of solid solutions on M (transition metal) and X (carbon or nitrogen) sites, control of surface terminations, and the discovery of ordered double-M MXenes offer the potential for synthesis of dozens of new materials. This presentation will describe the synthesis of MXenes, their and assembly into films and 3D structures. Their properties and applications in energy storage and electrocatalysis will be discussed.

Over the last decade, the cost of photovoltaic solar energy conversion has dropped very dramatically with solar photovoltaics “now the cheapest source of electricity in most countries” and “now offering some of the lowest cost electricity ever seen”, according to the International Energy Agency. However, improvements are in the pipeline that are leading to an era of “insanely cheap” solar power, within the coming decade.

The developments leading to these cost reductions will be described as well as the pending improvements that will allow solar to continue on its trajectory to even lower future costs over the remainder of this decade.

An example of the impact of these cost reductions is included as Figure 1. This shows both the history of the lowest bids received internationally for the supply of electricity using photovoltaics under power purchase agreements (PPAs), as compiled by the author, together with the global average solar PPA contract, as compiled by IRENA. These averages include systems such as in Japan where prices are incredibly high compared to other countries. Also shown, for comparison, are the lowest bids received at a 2016 Chilean auction for the supply from more traditional sources, as a reference.

Figure 1: History of solar photovoltaic electricity prices as revealed through PPA bids and contracts.

The rapid reduction in the lowest PPA bids post-2016 stem from the introduction of new photovoltaic technology, specifically the PERC cell (passivated emitter and rear cell) invented by the author and developed by his team. PERC now accounts for over 90% of global photovoltaic production, offering not only higher sunlight conversion efficiency but also new functionalities, such as bifacial operation allowing stray light on the module rear to be converted at essentially no extra cost. The lowest PPA bid received to date was US$10.40/MWh (1c/kWh!) in Saudi Arabia in 2021.

Keywords: Dynamic Monitoring and Decision Systems (DyMonDS); social-ecological energy systems (SEES); cyber physical systems (CPS); digitization; decarbonization.

In this talk we explore how today's operations of electric power grids can be enhanced by evolving a hierarchically-designed and operated physical system into an interactive Cyber-Physical System (CPS). Today, the operation is fundamentally coordinated by the Energy Management Systems (EMS) sending commands to controllable power plants in their area to produce energy in a feed-forward manner. This is done at the Balancing Authority (BA) level where EMS uses its SCADA-enabled state estimator to predict power imbalances. The hard -to-predict imbalances are managed by the BAs, most often implemented using dedicated communication and control schemes.

Important for understanding new opportunities for digitization is to understand the assumptions implied in today’s operation and to design hardware and software needed to relax them. The emerging poly-centric approach to electricity services is described as a possible way forward [1]. The next generation SCADA becomes a Dynamic Monitoring and Decision System ( DyMonDS) which relaxes major assumptions through interactive information exchange [2,3]. This brings about inter-temporal and inter-spatial flexibility as a means of implementing cooperative gains and the ability to increase efficiency without sacrificing QoS. This CPS design is non-unique for any given social-ecological energy system (SEES) since it depends on the performance objectives and its resources, end users, governance system and their interactions. System governance and policy making determine the overall organization of the physical system into sub-systems with their own sub-objectives, and rules for information sharing in operations and planning. As such, they must be accounted for when building physical man-made portions of the system and the supporting CPS architecture. Design of a man-made physical grid and its cyber are done to enhance the performance of an existing man-made system. At the same time, digitization is needed to improve dynamic interactions of the SEES components and to align their sub-objectives to the best degree possible. Several real-world power grid examples are shown to illustrate its key role and potential benefits.

References
[1] https://www.dropbox.com/s/2s4bgcr4bympq3b/Ilic_Lessard_EESGatMITWP_dec302020%20-%20Copy.pdf?dl=0.
[2] - Ilic, Marija D. "Toward a unified modeling and control for sustainable and resilient electric energy systems." Foundations and Trends® in Electric Energy Systems 1.1-2 (2016): 1-141.
[3] – Ilić, M. D. (2010). Dynamic monitoring and decision systems for enabling sustainable energy services. Proceedings of the IEEE, 99(1), 58-79.

The shift to more-electric cars and transportation brings opportunities for control, extreme performance, energy reduction and flexibility, cheaper operation, and lower emissions. Customers see limited range, battery performance limits, slow refueling, and lack of charging facilities as big drawbacks. This presentation shows how to simplify infrastructure requirements. The energy needs of electric and plug-in hybrid passenger cars can be met with conventional single-phase electrical outlets. Safety protection, metering, billing, and other functions can be supported by a car to turn a “dumb” electrical outlet into a smart vehicle charge point. Flexibility supported within a vehicle can minimize carbon impact and enhance environmental benefits. Actual driver needs are discussed, showing how more advanced chargers fit in and why “slow charging” is a fallacy most of the time. The results provide perspective to the context of present intensive effort on fast charging. Survey results on the University of Illinois campus help to support the ideas. The talk explores how to think differently about electric cars, energy, and how infrastructure interaction can work. Flexibility can make electric vehicles important partners for low-carbon power grids.

Keywords (max 5 related to your abstract): renewable energy, clean energy, energy infrastructure, energy platform, energy storage

Today fossil energy dominates energy consumption across the world. There has been an increasing momentum to reduce fossil energy consumption and increase renewable energy utilization. Such high penetrations of distributed renewable resources bring large uncertainty and complexity that cannot be easily handled by the current infrastructure. Here we discuss a platform-based approach, called the energy platform as a viable solution for addressing the renewable energy challenges. The energy platform consists of an array of computational algorithms, sensing and control technologies for key industry, energy generators and users to jointly manage and control the complex energy infrastructure. The energy platform also requires breakthroughs in many areas, including large scale energy storage, efficient power electronics, sensors and controls, new mathematical and computational tools, and deep integration of energy technologies and information sciences to control and stabilize such complex systems.

We are developing green technologies to benefit sustainable environment, which will enable people and the environment to prosper together. The Center for Filtration Research (CFR) at the University of Minnesota, collaborating with 20 leading international filtration manufacturers and end users, was established to find filtration solutions to mitigate PM_2.5 and other environmental pollutants. CFR investigators perform fundamental and applied research on air, gas and liquid filtration. There are more than 15 on-going research projects performed at CFR. I will select 6 projects to demonstrate the scope of the research topics: 1. Reduction of aerosol concentration in classrooms under various HVAC conditions to prevent virus transmissions; 2. Filtration performance improvement using beaded nanofiber; 3. Ozone removal using Zeolite catalysts; 4. Saliva evaporation experiment at low pressure environment; 5. Development of a microsensor for real-time detection of bioaerosols and particles in bulk liquids and aerosols; 6. Temperature resistant nano-scale membrane for enhanced ceramic wall-flow filter performance.

Large scale air cleaning towers are established in Xi’an and Yancheng in China, and two additional towers in Delhi, India. They are developed to mitigate PM2.5 pollutants in urban air. The second-generation tower in Yancheng is developed to reduce not only the PM_2.5 but also CO₂ in the atmosphere. All these research and development activities are helping to improve sustainable environment.

Figure 1: Three generations of air cleaning towers for urban pollution control and CO2 mitigation.

While much progress has been made to scaling solar technologies in the field, there remains a massive further (costly, and energy-intensive) build to be completed to meet the global community’s ambitious net zero 2050 goals. Electrifying fuels and chemical synthesis is less far along, with the technologies for CO2 capture and utilization/upgrade still seeing ongoing development and the subject of fundamental scientific research. I will overview progress in each and then propose some targets and exciting directions for these intertwined topics.

Metal halide perovskites are a relative newcomer to the field of PV research, however more than ten years has passed since the first publication of metal halide perovskites use as a “sensitizer” in a solar cell, and 2022 marks ten years since 10% efficient solid-state lead halide perovskites solar cells were realised and the flourishing filed of perovskite photovoltaics began. In this talk I will highlight some of the key advances we have made in researching metal halide perovskites, with a specific focus upon materials and device stability. I will highlight why moving to higher PV cell efficiency is an important path forward for the industry and I will then focus upon the opportunities and challenges for multi-junction perovskite solar cells, which have already delivered efficiencies surpassing silicon PV, and show a pathway to achieve highly efficient wide band gap perovskites, required for multi-junction applications. I will finally discuss commercialisation efforts on the path towards industrialising the perovskite-on-silicon tandem technology.

Hassan Raza¹,. Songyan Bai²,. Junye Cheng³,. Soumyadip Majumder¹, He Zhu⁴,.Qi Liu⁴,. Guangping Zheng¹,.Xifei Li^5,6, Guohua Chen^1,7,*
1 Department of Mechanical Engineering, Research Institute for Smart Energy, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China
² State Key Laboratory of Photocatalysis on Energy and Environment, College of Chemistry, Fuzhou University, Fuzhou, Fujian, 350108 China
³ Department of Materials Science, MSU-BIT University, Shenzhen, Guangdong Province 517182, P. R. China
⁴ Department of Physics, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, China
⁵ Xi'an Key Laboratory of New Energy Materials and Devices, Institute of Advanced Electrochemical Energy, School of Materials Science and Engineering, Xi'an University of Technology, Xi'an, Shaanxi 710048, China
⁶ Center for International Cooperation on Designer Low-carbon & Environmental Materials (CDLCEM), Zhengzhou University, Zhengzhou, Henan, 450001, China
⁷ School of Energy and Environment, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, China, guohchen@cityu.edu.hk

Keywords: Electrolyte, Metal-organic frameworks, Polysulfide, Sulfur-carbon composite, Shuttle effect

Abstract

To realize a low-carbon economy and sustainable energy supply, the development of energy storage devices has aroused intensive attention. Lithium-sulfur (Li-S) batteries are regarded as one of the most promising next generation battery devices because of their remarkable theoretical energy density, cost-effectiveness, and environmental benignity. However, the practical application of Li-S batteries is hindered by such challenges as low sulfur utilization (<80%), fast capacity fade, short service life (<200 redox cycles), and severe self-discharge. The reasons behind the challenges are: i) low conductivity of the active materials, ii) large volume changes during redox cycling, iii) serious polysulfide shuttling and, iv) lithium-metal anode contamination/corrosion and dendrites formation. Significant achievements have been made to address these problems in the past decade. In this review, the recent advances in material synthesis and technology development are analyzed in terms of the electrochemical performances of different Li-S battery components. The critical analysis was conducted based on the merits and shortcomings of the reported work on the issues facing the individual component. A versatile 3D printing technique is also examined on its practicability for Li-S battery production. The insights on the rational structural design and reasonable parameters for the Li-S batteries are highlighted along with the “five 5s” concept from a practical point of view. The remaining challenges are outlined for researchers to devote more efforts on the understanding and commercialization of the device in terms of materials preparation, cell manufacturing, and characterization [1].

References
[1] – Raza et al., “Li-S Batteries: Challenges, Achievements and Opportunities”, Submitted to Electrochemical Energy Reviews, 2022.

Highly efficient and low-cost perovskite solar cells (PSCs), one of the most promising next-generation photovoltaic technology, triggered intensive research around the world. Up till now, PSCs have achieved the record power conversion efficiency of 25.7% and the device stability has been improved substantially. To push forward the development of PSCs, researchers from home and abroad have been overcoming the obstacles of commercialization. According to our estimation of the levelized cost of electricity, the key to future applications is to reduce the cost of PSCs which strongly depend on high efficiency and long stability. In this presentation, I will introduce our recent works on promoting the efficiency and stability of PSCs from aspects of crystallization, passivation, and ion-migration blocking.

We introduced a perovskite crystal array (PCA) with regular distribution to assist the growth of the perovskite absorption layer. The PCA provided nuclei where the crystallization can commence without overcoming the critical Gibbs free energy for nucleation and induces a controllable bottom-up crystallization process under solvent annealing. As a result, the device achieved power conversion efficiency of over 25.1%. Furthermore, we constructed a composite electrode of copper-nickel (Cu-Ni) alloy stabilized by in situ grown bifacial graphene. The device with the copper-nickel electrode showed an efficiency of 24.34% (1cm²) and stability: 95% of their initial efficiency is retained after 5,000 hours at maximum power point tracking under continuous 1 sun illumination.

References
[1] Shen et al., Energy Environ. Sci., 15, 1078(2022).
[2] Luo et al., Adv. Mater. 2022. Online, DOI: 10.1002/adma.202202100.
[3] Su et al., Sci. China Chem., 65, 1321 (2022).
[4] Lin et al., Nature energy, 7, 520 (2022).

Organic solar cell (OSC) is a very promising photovoltaic technology. Over the past decades, the power conversion efficiencies (PCEs) of OSCs have been promoted from about 1% to currently over 19% for single-junction devices and over 20% for double-junction tandem devices. The development of new organic photovoltaic materials, including donor, acceptor and interlayer material, contributed greatly to the rapid increase of PCEs. A variety of effective molecular design and aggregation structure control methods have been developed to optimize the molecular energy levels, absorption spectra, mobility and phase separation morphology of the photovoltaic active layers. In this presentation, some general and efficient molecular design strategies related to these two polymer donors will be summarized and introduced. What is more, some of our recent progress including the single-junction OSCs with over 19% PCE and the double-junction tandem OSCs with over 20% PCE will be briefly introduced.

Figure 1: Photovoltaic characteristics of the highly efficient single- and double-junction organic solar cells.

Reclamation and marine infrastructure projects often adopted simple artificial vertical or slope seawalls as coastal defences against wave action, flooding and land erosion. However, these structures do not possess any microhabitats that can be readily occupied and used by marine organisms as refuges and feeding grounds. Through incorporating the knowledge of marine ecology and collaboration with ecologists and architects, engineers now are able to design eco-friendly artificial structures to serve dual roles as coastal defences and functional ecosystems for enhancing marine biodiversity and ecosystem services such as carbon squassation and biofiltration. In this lecture, I will introduce the basic ecological principles for eco-engineered shorelines and draw examples from different parts of the world. I will also highlight the results of several recent trials of eco-engineered shorelines in Hong Kong.

Carbon neutrality is recognized as an urgent global issue. The International Energy Agency (IEA) has reported that increasing the end-use energy efficiency is the best strategy to reduce carbon emission. Many countries and cities have set challenging targets for energy saving as it represents one of the most significant contributions to achieve net zero.

Among various energy consumers, the thermal energy consumers, such as air-conditioning, space heating, hot water, dehumidification, etc. play the dominating role. All of the above commonly reject large amount of low-temperature waste heat (< 80 deg C) during normal operation. The waste heat can be directly used for preheating water. However, our hot water demand is relatively a lot lower than the waste heat available. Therefore, we have developed modified organic Rankine cycle (ORC) to convert the low-temperature waste heat into electricity supply. The innovative system design involves the integration among vapor compression refrigeration cycle, heat pump and Rankine power cycle into a single multi-functional thermodynamic cycle. Nanostructured biphilic surfaces designed for coalescence-induced jumping droplets are employed to enhance the heat exchangers. The system is controlled to operate at the optimal condition for maximum energy efficiency.

Figure 1: Modified organic Rankine cycle (ORC) for low-temperature waste heat recovery

References
[1] – Z. Zheng, J. Cao, W. Wu, M.K.H. Leung, 2022, Parallel and in-series arrangements of zeotropic dual-pressure Organic Rankine Cycle (ORC) for low-grade waste heat recovery, Energy Reports 8, p. 2630-2645.
[2] - Z. Zheng, X. Hong, W. Wu, Y. Feng, M.K.H. Leung, 2022, Exploring low-grade heat in exhaust gases with moisture via power generation cycles, Journal of Cleaner Production, Vol. 357, 131892.
[3] - Yihao Zhu, C.Y. Tso, Tsz Chung Ho, Michael K.H. Leung, Shuhuai Yao, 2021, Coalescence-induced jumping droplets on nanostructured biphilic surfaces with contact electrification effects, ACS Applied Materials & Interfaces 13, 9.
[4] - J. Cao, X. Hong, Z., Zheng, M. Asim, M. Hu, Q. Wang, G. Pei, M.K.H. Leung, 2020, Performance characteristics of variable conductance loop thermosyphon for energy-efficient building thermal control, Applied Energy 275, 12, 115337.

Energy storage system is a critical enabling factor for deploying unstable and intermittent renewable power sources, such as solar and wind power sources. Non-aqueous lithium ion batteries dominate the battery markets owing to its high energy density. However, they are flammable, which could bring catastrophic damages in large-scale applications. Redox flow batteries are promising technologies for large-scale electricity storage, owing to its design flexibility in decoupling power and energy capacity. However, redox flow batteries have been suffering from low energy density, which significantly decreases its competitiveness for both stationary and transportation applications. In this presentation, we will discuss strategies to improve the safety, energy density, and cycle life of Li-ion batteries and redox flow batteries. Ultimately, we aim to enable stable and efficient high-energy-density energy storage systems to address the intermittency of the renewable power sources. This will bridge the gap between intermittent renewable power supplies and power demands in grid-storage and electric-vehicles.

The penetration of power electronics into power generation and distribution systems has deepened in recent years, as prompted by the increasing use of renewable sources, the quest for higher performance in the control of power conversion, as well as the increasing infl-uence of economic plans that necessitate power trading among different regions or clusters of power distribution. As a result of the increased use of power electronics for controlling power ¬flows in power systems, interactions of power electronics systems and conventional synchronous machines’ dynamics would inevitably cause stability and robustness concerns, which can be readily understood by the coupling effects among interacting dynamical systems of varying stability margins (or transient performances)_[1]. In this talk, we discuss the various problems of power electronics penetration into power grids and the implications on the stability and robustness of power networks, and examine the current progress and future direction of research in power systems amidst the extensive deployment of power electronics.

Reference:
[1] C. K. Tse, M. Huang, X. Zhang, D. Liu, and X. L. Li, "Circuits and systems issues in power electronics penetrated power grid," IEEE Open Journal of Circuits and Systems, vol. 1, pp. 140-156, September 2020.

As global IT traffic continues to grow at double-digit annual rates, the underlining hardware in contemporary optical and wireless networks is facing increasing challenges in the footprint, power consumption and cost. Photonic integrated circuits could address these challenges by simultaneously integrating many optical components on a single photonic chip. Among various photonic material platforms, lithium niobate (LN) is a particularly attractive candidate due to its strong electro-optic effect, wide transparency window and low optical loss. While LN has been widely deployed in the telecommunications industry for decades, the material has long been perceived as one that cannot be integrated due to difficulties associated with its nanofabrication. In this talk, I will first discuss our efforts in LN device fabrication techniques that have enabled thin-film LN devices and circuits that simultaneously feature sub-wavelength light confinement, low propagation loss and wafer-scale fabrication capability. Based on this platform, we have demonstrated a series of power-efficient integrated photonic components, including electro-optic modulators with CMOS-compatible drive voltages and electro-optic bandwidths covering the entire millimeter-wave band, ring-assisted Mach-Zehnder modulators with ultrahigh linearity, low-power-consumption frequency-comb generation, as well as efficient wavelength converters. The excellent device performances, together with the low optical loss and wafer-scale processes, could enable a variety of energy-efficient applications in future intra- and inter-datacenter optical links, microwave and millimeter-wave photonics, as well as analog and neuromorphic optical computation.

References
[1] - C. Wang , M. Zhang*, X. Chen, M. Bertrand, A. Shams-Ansari, S. Chandrasekhar, P. Winzer, and M. Lončar “Integrated lithium niobate electro-optic modulators operating at CMOS-compatible voltages”, Nature, 562 (2018): 101-104.
[2] - M. Zhang*, B. Buscaino*, C. Wang*, A. Shams-Ansari, C. Reimer, R.R. Zhu, J. M. Kahn and M. Lončar “Broadband electro-optic frequency comb generation in a lithium niobate microring resonator” Nature, 568 (2019): 373-377.
[3] - M. Zhang*, C. Wang*, Y.W. Hu, A. Shams-Ansari, T.H. Ren, S.H. Fan & M. Lončar “Electronically programmable photonic molecule”, Nature Photonics, 13 (2019): 36–40.
[4] - C. Wang*, M. Zhang*, M.J. Yu, R.R. Zhu, H. Hu and M. Lončar “Monolithic photonic circuits for Kerr frequency comb generation, filtering and modulation”, Nature Communications, 10 (2019): 978.
[5] - Z.X. Chen, Q. Xu, K. Zhang, W.H. Wong, D.L. Zhang, E.Y.B. Pun & C. Wang, “Efficient erbium-doped thin-film lithium niobate waveguide amplifiers”, Optics Letters, 46 (2021): 1161-1164.
[6] - Z.X Chen, J.W. Yang, W.H. Wong, E.Y.B. Pun, and C. Wang, “Broadband adiabatic polarization rotator-splitter based on a lithium niobate on insulator platform”. Photonics Research, 9:2319-2324, 2021.

Over the past few years, organic-inorganic hybrid perovskites have emerged as a new class of solution processable semiconductor for many optoelectronic applications, such as solar cells and LEDs. Their electronic, electrical and optical properties can be controlled by tuning their compositions and crystal structures. In this talk, I will discuss how to control the dimension and nanostructure of perovskites by introducing small molecules and polymers with tailored functional groups that can strongly interact with the perovskite crystals (Fig.1). Using such strategy, we have developed very stable quasi-2D perovskite solar cells^[1] with much improved stability and efficiency as well as highly efficient blue^[2] and white^[3] emitting perovskite LEDs. I will also discuss how to lean on the experience in interface engineering for organic solar cells and design new electron and hole transport conjugated polymer materials with proper interfacial properties to provide surface defeat passivation functionality and improve the charge collection efficiency of perovskite solar cells,^[4-6] as well as organic/perovskite tandem solar cells.^[7]

Figure 1: Schematic illustration of the two types of interfaces that can be molecularly engineered in perovskite optoelectronic devices.

References
[1] Q. Yao, H.-L. Yip, et al, Adv. Mater. 2020, 32, 2000571
[2] Z. Li, H.-L. Yip, et al, Nat. Commun. 2019, 10, 1027
[3] Z. Chen, H.-L.Yip, et al, Joule, 2021, 5, 456
[4] J. Tian, Q. Xue, H.-L. Yip, et al, Adv. Mater. 2019, 31, 1901152
[5] J. Wang, Z. Zhu, H.-L. Yip, A. K.-Y. Jen, Nat. Commun. 2020, 11, 177
[6] T. Niu, Q. Xue, Y. Li, H.-L. Yip, et al, Joule., 2021, 5, 249
[7] Y. Xue, Q. Yao, H.-L. Yip, et al, Adv. Funct. Mater., 2022, 32, 2112126

China’s commitment to carbon neutrality before 2060 came as a complete surprise to both international and Chinese communities. To achieve both carbon peak and carbon neutrality requires huge capital investment in the field of renewable energy, cross-regional power transmission, advanced energy storage, charging stations and hydrogen refueling stations in the transportation field, end-use electrification, green buildings, and energy saving and emission abating. A variety of studies project different outcomes, but all the forecasts for required investment exceed CNY 100 trillion over the next 40 years. Government finance can only cover a small portion of such a huge scale of investment, and the significant gap must be made up by social capital, which must be guided by market-oriented approaches. The carbon market can just play such a role in providing market carbon price signals, incentivizing and attracting resources to tilt towards low-carbon green projects, promote green and low-carbon development, and achieve the aforementioned dual carbon goals while helping entities cut emissions at the least cost.

Against this background, China launches the national carbon market with the power generation sector initially being covered. Since it began its first trading on 16 July 2021, the national carbon market has operated more than one year, and all entities covered had experienced one compliance cycle by the end of December 2021. It is a good time to evaluate the operation of China’s national carbon market and show how the market will go in the near future.

This presentation will show how China’s national carbon market operates, what characteristics we can observe from its operation, how does China’s carbon market compare with the EU carbon market, what challenges it faces, what does the construction of united national market mean for carbon market, what are the focuses of the national carbon market development, what will the existing carbon pilots do to strengthen the effects of national carbon market, how does carbon market integrate with power market to achieve the desired outcomes, what are the implications of the EU border carbon adjustment mechanism? The better understanding of all these issues helps to understand the development and role of China’s national carbon market in meeting the aforementioned dual carbon goals.

The CLP Group is an investor and operator in the Asia-Pacific energy sector with investments in Hong Kong, Mainland China, Australia , India, Southeast Asia and Taiwan that span across the energy supply chain. The company first brought nuclear energy to Hong Kong in 1994 through the investment in the Daya Bay Nuclear Power Station, the first large-scale commercial nuclear power station in China. Since then, nuclear energy has been safely and reliably meeting a significant part of Hong Kong’s energy needs. Nowadays, a quarter of Hong Kong’s electricity demand is powered by nuclear energy imported from Daya Bay Nuclear Power Station.

In joining global efforts on combating climate change, the short talk will introduce how CLP, as one of the major energy providers in Hong Kong and the Asia-Pacific region, sets its vision and goal to decarbonise its business in a longer term, and how nuclear energy has been playing a key part in the journey. The presentation will talk about nuclear power’s benefits to Hong Kong and to CLP as an investor and off-taker. Amid the latest nuclear energy development worldwide, in particular the rapid development in China in recent decades, the talk will also share views on future opportunities offered by nuclear energy to Hong Kong in the energy transition journey.

Climate finance in various forms such as ESG investing and carbon emissions trading, has become mainstreamed globally. The market mechanisms do not reduce carbon emissions themselves but can potentially incentivize the invention and deployment of technologies and practices, and achieve economic efficiency in climate mitigation and adaptation. Unfortunately, the effectiveness of those market mechanisms has been largely compromised by a lack of integrity in the monitoring/measurement, verification and reporting of ESG performance and carbon emissions embedded in business operations. The third parties are contracted to provide carbon emissions data for regulators, green investors, and the public, who are the principals financing climate actions and bearing the consequences of climate change. Thus, the integrity of the information and data supporting system is a function of the institutional design of environmental monitoring and reporting, especially how the principal-agent problem has been dealt with, which is context specific. Because carbon and air pollution reduction complement each other and face common challenges, it is beneficial to unpack the contractual relationships in both to inform institution building for achieving carbon neutrality and local health co-benefits in China.

According to transaction cost economics, the principal bears the following three contractual hazards, asset specificity, observability and enforceability, which are contingent upon the ex ante screening, contract design and execution, and ex post evaluation. The centralization and marketization reform in air quality monitoring in 2015 was found to be partially effective in addressing asset specificity and enforceability. However, resorting to the market is not a panacea because the emitters and local government are still motivated to form a shadow clientele relationship with those qualified data providers, given climate finance and government responsibility system offer economic gain and career prospects, respectively. The public interest litigation initiated by the China Federation for Environmental Protection in July 2022 against the two consulting firms for falsifying carbon emissions data offers ad hoc evidence on the perennial challenge of holding the agents accountable for environmental data provision that sets necessary foundation for climate finance to work. A country-wide systematic review is in order to stocktake and diagnose contract terms and practices of the environmental monitoring services industry, given the regional variations in local contexts and the power and reach of the local government. Without the ground work, it is impossible to build necessary institutions and a professional work force for creating a level playing field and achieving carbon neutrality in the future.

Hydrogen production from photocatalytic water splitting under visible light has been considered a potential alternative to make solar energy storable and transportable. Oxide photocatalysts are perhaps the most popular and promising class of materials for water splitting, either via photocatalytic or photoelectrochemical pathways. Typically, oxide photocatalysts possess deep and energetic valance band, endowing them with impressive oxidative performance (such as water oxidation to O₂, oxidative organic degradation). The conduction band of oxides is relatively mild in reducing capability and often in needs of other modification (such as doping and introduction of co-catalyst). By manipulating the band structures of photocatalysts, the redox performance can be improved and the product selectivity can be modulated. Our group is interested in the phenomena of charge transportation in semiconductors upon photoexcitation. Fascinated by its complexity, the tuning of band structure to strengthening or weakening certain half reaction of redox, together with the design of defects or surface states on photocatalyst, photoexcited electron-hole pairs can experience distinctive transportation behaviour. Those impacts can be used constructively in the targeted redox reaction (in this case, water splitting). Collectively studied over previous years, the group has accumulated some experience in understanding and controlling the charge behaviour of oxide photocatalyst.

In this talk, a general strategy in improving the shuttling of charges in bismuth vanadate (BiVO₄) will firstly be shared. Facet engineering and nanoscaling are generally adopted by the community. Subsequently, the originally weak conduction band of BiVO₄ can be uplifted through the introduction of quantum confinement effect. Conduction band is lifted sufficiently to enable proton reduction for H₂ generation. The original incapability in hydrogen production of BiVO₄ has now been extended into efficient hydrogen evolution. By careful surface functionalisation with suitable co-catalyst, overall water splitting using only BiVO₄ is achievable. Insights on such materials engineering will be discussed more thoroughly in the presentation.

References
[1] H. Wu, H. L. Tan, C. Y. Toe, J. Scott, L. Wang, R. Amal, Y. H. Ng, Advanced Materials, 32 (18), 1904717 (2020)
[2] H. Wu, R. Irani, K. Zhang, L. Jing, H. Dai, H. Y. Chung, F. F. Abdi, Y. H. Ng, ACS Energy Letters 6 (10), 3400-3407 (2021)

Nuclear power, with its low carbon nature, could be a very effective option for carbon neutrality in 2050-2060. Nuclear safety, which is strongly related to heat transfer, is the key to broaden the acceptance of nuclear power. Indeed, a severe accident like Fukushima Daiichi one results from poor heat transfer due to loss of coolant or flow while the nuclear fuel elements are still releasing significant amount of decay heat. This talk presents some of our innovative heat transfer studies to enhance nuclear safety.

We explored natural seawater as an alternative emergency coolant for nuclear power plants located at seashore. The quenching of hot metal spheres, up to 1000 °C, in natural seawater at room temperature was investigated. Unlike that in de-ionized water, the study reveals that film boiling is completely suppressed in natural seawater leading to much more rapid quenching in natural seawater than that in de-ionized water. This demonstrates the beneficial side of using natural seawater, which is abundant for nuclear power units located at sea coast, as an alternative emergency coolant to enhance nuclear safety. Currently, we are exploring the two-phase natural circulation of artificial seawater, which could provide passive cooling for reactor core. Bubble foam is found to be typical for boiling in seawater due to lack of bubble coalescence resulting in significantly different two-phase natural circulation phenomena.

In addition, a new concept of heat transfer design promoting nuclear safety is proposed. Recently, we have developed a Counter Flow Diverging Microchannel (CFDM) heat sink with ultra-high performance through an innovative combination of diverging microchannels and counter-flow manifold. Such a counter flow with diverging channel design enables extensive channel-to-channel heat transfer and may result in a void fraction distribution nearly uniform along the channel at high heat fluxes. Consequently, the critical heat flux may be significantly increased, while the two-phase flow pressure drop may not increase significantly with increase in heat flux. Such a high performance and robust heat transfer concept may be considered for an innovative design of a steam generator or reactor core. The thermal margin to the critical heat flux may be significantly enhanced and, therefore, nuclear safety as well.

References
[1]. S.-H. Hsu, Y.-H. Ho, M.-X. Ho, J.-C. Wang and Chin Pan*, “On the Formation of Vapor Film during Quenching in De-ionized Water and Elimination of Film boiling during Quenching in Natural Sea Water”, International Journal of Heat and Mass Transfer, 86, 2015, 65-71.
[2] X. Jiang, S. Zhang, Y. Li, Z. Wang, Chin Pan*, Achieving Ultra-high Coefficient of Performance of Two-phase Microchannel Heat Sink with Uniform Void Fraction, International Journal of Heat and Mass Transfer, 184, 2021, doi: https://doi.org/10.1016/j.ijheatmasstransfer.2021.122300

With the development of economy, the energy consumption of air conditioning systems has become a major concern. This problem is more serious in Hong Kong, which is located in the subtropical region and has a hot and humid climate. Therefore, the research and development of green building technologies for air conditioning energy-saving plays a vital role in addressing the issues of climate change and energy crisis for both Hong Kong and the world. In this talk, we present a new technology that combines passive radiative cooling and thermochromic smart windows to provide new insights for building energy saving. Specifically, the patented passive radiative cooler is applied to the roof and exterior walls, which can reflect almost all sunlight while emitting mid-infrared thermal radiation to the cold universe, thereby achieving an "electrical-free cooling" effect. We have fabricated a passive radiative cooling ceramic tile, showing a strong solar reflectivity (99%) with high mid-infrared emissivity (95%). A local field test has also been conducted in which the surface temperature of the cooling ceramic tile is ~10 °C lower than a commercial white ceramic tile with a cooling power of 130 W/m². In addition, the thermochromic smart windows can automatically change their color subject to the ambient temperature, intelligently tuning the heat gain and loss through the windows, so that the indoor environment can be warm in winter and cool in summer. Specifically, we have developed a near-infrared-activated thermochromic perovskite smart window in which the window can selectively absorb near-infrared to generate heat and activate the thermochromism of perovskite, smartly modulating the solar heat gain from the window. This high-level smart window demonstrates reversible color change with a transmittance of τlum = 65.7% and 25.6% at the cold and hot states, smart solar modulation ability of Δτsol = 17.5%, strong near-infrared absorption of ANIR = 78.2%, and low emissivity of ε < 0.3. Importantly, for the first time, under natural sunlight without any atmosphere control strategies, a self-activated reversible thermochromic cycle is successfully observed in the field test, which is highly desired in practical applications. Moreover, a large 8 °C indoor air temperature reduction is achieved by using the window. Overall, combining with passive radiative cooling and thermochromic smart window technologies, the cooling load of air conditioning can be effectively reduced, achieving significant building energy saving and carbon reduction. The technologies will not only reduce energy consumption and help address the problem of climate change but also bring innovative ideas to the green building industry, promoting economic development and carbon neutrality globally

Hybrid organic-inorganic halide perovskites are remarkable materials with combined features of hard and soft matters, which show great potential for photovoltaic and optoelectronic applications. In this talk, I will present our recent works on manufacturing high-efficiency, stable and environmentally friendly PSCs using an integrated approach to design and develop novel compositionally engineered stable perovskite absorbers with tailored cations/anions and tailor-made charge transport/extraction layers. To enhance the perovskite absorber stability, functionalized organometallic interfacial materials were developed to create suitable interfaces. Further improvements of PCE and stability can be obtained by using molecular-engineered charge-transporting materials (CTMs) for efficient collection of electrons and holes. Finally, to realize the environmentally friendly PSCs, surface coating and novel encapsulation that can physically or chemically capture the leaked Pb ions from degraded devices will also be integrated into the PSCs.