硅酸盐学报2025，Vol.53Issue(10)：3056-3068,13.DOI:10.14062/j.issn.0454-5648.20250187
高温质子陶瓷电化学合成氨关键材料的研究进展
Research Progress on Key Materials for High-Temperature Electrochemical Ammonia Synthesis by Proton-Conducting Ceramic
摘要
Abstract
As the second largest chemical product globally,ammonia plays a pivotal role in the economy.The conventional Haber-Bosch process urgently needs innovation due to its high energy consumption and environmental pollution.The high-temperature electrochemical ammonia synthesis system based on protonic ceramic cells,which uses electric energy to overcome the thermodynamic barrier of nitrogen activation and achieves green synthesis under ambient pressure conditions,has attracted much attention. Proton-conducting ceramic cells consist of an electrolyte and two electrodes(i.e.,ammonia electrode and hydrogen electrode).The electrolyte must simultaneously fulfill dual functions,i.e.,proton conduction and gas isolation.Its material design requires a)dense microstructure to block gas permeation,b)high proton conductivity and negligible electronic conductivity,c)chemical stability under high-temperature conditions with exposure to H2O,CO2,and NH3,and d)thermal expansion coefficient compatibility with electrode materials to avoid thermomechanical stress-induced damage.This review systematically represents the applications of perovskite,fluorite,and pyrochlore-type electrolytes in ammonia synthesis.SrCeO3-based oxides are the reported perovskite materials with a proton conductivity,with their proton transport capacity that is enhanced through ionic doping strategies.Compared to other perovskite oxides,BaCeO3-based perovskites with a higher conductivity are currently among the most extensively studied proton-conducting materials.Doping with rare-earth metals is a common strategy to improve the proton conductivity of BaCeO3-based oxides.Alkaline-earth zirconate oxides(i.e.,CaZrO3,SrZrO3,BaZrO3)exhibit lower proton conductivity than cerium-based oxides but demonstrate superior chemical stability and mechanical strength.LaGaO3-based oxides achieve a nearly pure proton conductivity in H2 atmospheres,and LaGaO3-based electrolytes doped with Ca2+,Sr2+,or Ba2+demonstrate a good performance in ammonia synthesis.Beyond perovskites,non-perovskite oxides such as fluorite(i.e.,AO2)and pyrochlore(i.e.,A2B2O7)also exhibit a notable proton conductivity under high-temperature and hydrogen-containing conditions.Rare-earth-doped CeO2 fluorite-type electrolytes outperform perovskite counterparts in ammonia generation rates.SDC electrolyte achieves a record-high ammonia formation rate of 8.2×10-9 mol·s-1cm-2 at 650 ℃ as the maximum reported value based on proton-conducting ceramic.Pyrochlore-structured electrolytes have a proton conductivity comparable to fluorite structures but with enhanced chemical stability. The catalytic activity and stability of the ammonia electrode directly affect the rate of ammonia synthesis.Electrode materials require superior nitrogen adsorption/dissociation capabilities coupled with a high NH3 selectivity.Also,ammonia electrodes must demonstrate adequate electronic/protonic conductivity and chemical stability.Noble metals are widely used in early-stage proton-conducting ceramic electrochemical ammonia synthesis due to their high electronic conductivity and catalytic activity.Ag-Pd bimetallic alloys are the most common electrode materials.Pd exhibits a high catalytic activity for NRR,enabling N≡N bond dissociation at elevated temperatures.However,Pd preferentially adsorbs H atoms over N atoms,leading to dominant HER over NRR.Ag-Pd alloy partially suppresses HER,while enhancing ammonia production rates and faradaic efficiency.Perovskite materials become promising alternatives for ammonia electrodes due to their tunable structure,high thermal stability and low cost.Cobalt-based perovskites possess a superior catalytic activity,and they are extensively studied for electrochemical ammonia synthesis.However,some challenges such as cobalt reduction/volatilization,high thermal expansion coefficients,and elevated costs restrict their practical application.Ru-doped perovskites are particularly attractive due to the superior catalytic activity for N2 activation.Iron-containing perovskites have attracted much attention as cathode materials for protonic ceramic ammonia synthesis.The multivalent characteristics of Fe confer dual advantages in vacancy regulation and electronic structure optimization. Summary and prospects High-temperature proton-conducting ceramic ammonia synthesis remains in the fundamental research stage,requiring further studies in proton source optimization,material development,and reaction mechanism elucidation.For proton source exploration,previous studies predominantly used high-cost pure H2 as a proton source.Recent research has confirmed the feasibility of H2O as a proton source,but this imposes stringent requirements on electrode stability under steam exposure.Hydrogen derived from steam methane reforming or water-gas shift reactions offers an alternative strategy,enabling potential reductions in energy consumption and CO2 emissions.Future work should systematically evaluate the protonation efficiency of H2O,CH4,and other candidates,establishing a matching mechanism among hydrogen sources,electrolytes,and electrodes.Compared to conventional metal electrodes,perovskite electrodes exhibit unique advantages in cost-effectiveness and performance tunability.However,their catalytic activity and long-term operational stability require an enhancement.Strategies such as ionic doping,defect engineering,in-situ exsolution,and advanced synthesis techniques can optimize crystal structures,enabling electrodes with high activity and durability.The reaction mechanism of protonic ceramic ammonia synthesis remains unclear.In-depth studies on catalytic pathways and degradation mechanisms at ammonia electrodes are urgently needed.The density functional theory should be used to calculate N2 adsorption/activation energy barriers and proton transport pathways,establishing structure-activity relationships between catalyst electronic structures and NRR performance.In-situ X-ray photoelectron spectroscopy and in-situ transmission electron microscopy are used to analyze the proton migration process at the hydrogen electrode and N2 activation process at the ammonia electrode,and the DRT analysis is used to reveal the velocity determination steps under multi-field coupling conditions.These studies will provide a theoretical support for the construction of efficient and stable proton ceramic ammonia synthesis system.关键词
合成氨/质子陶瓷电解质/氨电极材料/钙钛矿/电化学Key words
synthesis of ammonia/proton ceramic electrolyte/ammonia electrode material/perovskite/electrochemistry分类
能源科技引用本文复制引用
王嘉宾,周露,杨烨,颜冬,李箭,贾礼超..高温质子陶瓷电化学合成氨关键材料的研究进展[J].硅酸盐学报,2025,53(10):3056-3068,13.基金项目
国家自然科学基金(52472202). （52472202）
