固体氧化物电解池氢电极材料研究进展OA北大核心CSTPCD

As a device capable of converting electrical energy into chemical energy,solid oxide electrolysis cell(SOEC)has superior characteristics such as high energy conversion efficiency,reversible operation capability,and environmental friendliness.The hydrogen electrode as the direct site for the hydrogen evolution reaction(HER)is a crucial component of SOEC.Excellent hydrogen electrode materials require a chemical-structural stability under high-temperature reducing atmosphere,outstanding electrocatalytic activity,long-term operational stability,and cost-effectiveness.To meet these requirements,various types of hydrogen electrode materials are developed.However,their performance stability issues are evident,necessitating the overcoming of these challenges through materials development aligned with the unique demands of SOEC materials.It is thus essential to provide a systematic discussion on aspects such as the hydrogen electrode reaction mechanism(i.e.,hydrogen spillover,oxygen spillover),material requirements,physicochemical properties of electrode materials,electrochemical performance,and material degradation.This will facilitate subsequent research endeavors in this field. This review introduced cermet-based hydrogen electrodes,exemplified by materials such as Ni-Zr0.92Y0.08O2(YSZ)and Ni-Gd0.2Ce0.8O2(GDC).Cermet hydrogen electrodes composed of Ni and ceramic phases are widely used due to their excellent electrocatalytic performance of Ni,good mechanical strength,and lower cost.However,some issues such as Ni oxidation,migration,agglomeration,carbon deposition,and poor redox cycle stability during electrolysis of H2O and CO2 operations restrict the application of Ni-based cermet.This compels to seek novel hydrogen electrode materials to address these challenges,leading to the proposal of perovskite,with perovskite oxides as a representative category.Perovskite oxide is mixed ionic-electronic conductors(MIEC)material,so the reactive region can be expanded to the entire surface of the whole electrode to reduce the activation resistance.Also,perovskite has an excellent resistance to carbon deposition,sulfur poisoning,and redox cycle stability.The A,B,and O sites have a potential to be replaced by other ions,and the above characteristics lead to a wide range of interest in perovskite-based materials.The physicochemical characteristics and the pros and cons of each type materials of perovskite,i.e.,single perovskite(ABO3,i.e.,La1-xSrxCrO3-δ,SrFeO3-δ,SrTiO3-δ),double perovskite(A2B2O6,i.e.,PrBaFe2O5+δ,Sr2Fe2-xMoxO6-δ),and Ruddlesden-Popper perovskite(RP,An+1BnO3n+1)were discussed.The review also provides a comprehensive discussion on various strategies for improving material performance,including A-site vacancy,A/B-site doping,in-situ exsolution,second-phase composites,and microstructure optimization.Other materials like spinel with good stability and conductivity are explored as the alternatives for hydrogen electrodes. Under electrolysis conditions,the degradation issues of Ni-based cermet materials primarily revolve around the oxidation,migration,agglomeration of Ni,and external poisoning by sulfur and silicon.The oxidation of Ni leads to deactivation and loss of electronic conductivity,necessitating the protection of Ni-based cermet electrodes via introducing a reducing gas.Furthermore,the oxidation,migration,and agglomeration of Ni can disrupt the original structure and composition distribution of the electrode,resulting in a poor cyclic stability of the cermet-based electrode during redox cycles.The deposition of carbon can block triple phase boundaries(TPBs),reduce active reaction sites,and disrupt the microstructure of the electrode.Simultaneously,trace impurities in the reaction gas,such as sulfur,have a pronounced poisoning effect on Ni metal.Measures such as alloying,introducing materials with a high ionic conductivity,and regulating electrode structure can effectively mitigate these deteriorative effects and slow down the degradation process. Summary and prospects The existing research on hydrogen electrode materials for SOEC involved the systematic theoretical and experimental studies.To commercialize hydrogen production through SOEC,it is still necessary to further investigate hydrogen electrode materials.At the mechanistic level,advanced characterization techniques,such as in-situ transmission electron microscopy and X-ray photoelectron spectroscopy,combined with first-principles calculation and distribution of relaxation time method,can be employed to investigate the reaction mechanisms of SOEC hydrogen electrodes.This approach guides subsequent development and application of electrode materials.The degradation of hydrogen electrode materials is a primary obstacle to the current commercialization of SOEC.The existing research predominantly focused on Ni-based metal ceramic hydrogen electrodes.For Ni-based metal ceramics,the main issues involve the oxidation,migration,and coarsening of nickel.Based on the fundamental mechanisms of electrode reactions,a comprehensive exploration of material degradation phenomena and their mechanisms is conducted.The severity of the impact of the mentioned changes on the elementary reactions of the electrode is assessed,and the corresponding improvement strategies are proposed.At the material level,it is essential to conduct in-depth studies based on the actual requirements of the electrodes.Combining theoretical predictions with experimental data,some performance-enhancing novel hydrogen electrode materials can be obtained through ion doping and in-situ exsolution for the regulation of electronic structure,charge carrier migration capability,and surface oxygen vacancy formation energy.At the application level,improvements in large-scale cell manufacturing process,optimization of the microstructure of Ni-YSZ electrodes,and the incorporation of high-performance catalytic materials such as perovskites using methods like ion liquid injection are crucial for advancing the practical application of SOEC.