Opportunity
Human activities, such as over-fertilization and fossil fuel combustion, have severely disrupted the global nitrogen cycle, leading to widespread environmental contamination. Nitrite (NO₂⁻), a key intermediate in this cycle, is a recognized carcinogen and poses significant health risks, including conditions like blue baby syndrome and hypertension. Concurrently, ammonia (NH₃) is an indispensable chemical for agriculture and industry and a promising carbon-free energy carrier. The traditional Haber-Bosch process for ammonia synthesis is energy-intensive, operating under high temperature and pressure, and contributes to greenhouse gas emissions. Electrochemical nitrite reduction reaction (NO₂RR) offers a promising route to simultaneously remediate nitrite pollution and produce valuable ammonia under mild conditions using renewable electricity. However, existing electrocatalysts for NO₂RR suffer from critical limitations, including low activity, poor selectivity towards ammonia, limited Faradaic efficiency, and unsatisfactory stability. These shortcomings stem from the complexity of the multi-step, proton-coupled electron transfer process and the difficulty in optimizing catalyst properties to effectively adsorb and stabilize various reaction intermediates. Therefore, there is a pressing need to develop advanced, high-performance electrocatalysts that can efficiently and selectively convert hazardous nitrite into ammonia, addressing both environmental and energy challenges.
Technology
The present invention addresses these challenges by providing an electrocatalyst composed of IrNi-based alloy nanostructures with an unconventional hexagonal close-packed (hcp) crystal phase. The core innovation lies in the precise crystal phase engineering and structural design of these nanomaterials. The catalyst features a unique architecture with a Ni-rich core and an Ir-rich shell, synthesized via a facile one-pot solvothermal method using metal precursors, oleylamine, oleic acid, and formaldehyde. This specific hcp phase, as opposed to the common face-centered cubic (fcc) phase, is crucial. It induces stronger Ir-Ni electronic interactions, which optimize the surface electronic structure. This optimization enhances electron transfer efficiency and modifies the adsorption energies of key reaction intermediates during NO₂RR. Furthermore, the hcp IrNi-based nanostructures demonstrate a superior ability to generate active hydrogen species (H) on their surface. This abundant H supply is critical for efficiently hydrogenating nitrogen-containing intermediates, thereby significantly reducing the energy barrier and overpotential required for ammonia formation. The technology enables the concurrent removal of nitrite contaminants and the highly selective synthesis of ammonia, achieving performance metrics that surpass conventional catalysts.
Advantages
- Achieves exceptionally high ammonia selectivity and yield, with a Faradaic efficiency of up to 98.2% and a yield rate of 34.6 mg h⁻¹ mg_cat⁻¹.
- Operates effectively at low overpotentials, enabling energy-efficient ammonia production with a high half-cell energy efficiency exceeding 50%.
- Demonstrates excellent catalytic durability, maintaining stable performance over at least 20 consecutive electrolysis cycles.
- The synthesis method is facile, reproducible, and scalable, using a one-pot process that is suitable for potential industrial production.
- The catalyst design, featuring an unconventional hcp phase and a core-shell structure, optimizes electronic properties and active site availability, leading to faster reaction kinetics.
- Exhibits robust performance across a wide range of nitrite concentrations and under different pH conditions (alkaline to neutral), enhancing its practicality for real-world wastewater treatment applications.
Applications
- Electrochemical remediation of nitrite-contaminated water sources, such as agricultural runoff and industrial wastewater.
- Decentralized and sustainable electrochemical ammonia synthesis as an alternative to the energy-intensive Haber-Bosch process.
- Integration with renewable energy systems (e.g., solar, wind) for green ammonia production and energy storage.
- Serving as a high-performance catalyst for other relevant electrocatalytic reactions, such as the hydrogen evolution reaction (HER).
- Fundamental research in nanomaterials, crystal phase engineering, and electrocatalysis for nitrogen cycle management.
