Improving the activity and stability of Ni-based electrodes for solid oxide cells through surface engineering:Recent progress and future perspectives

Solid oxide cells(SOCs)have attracted great attention in the past decades because of their high conversion efficiency,low environmental pollution and diversified fuel options.Nickel-based catalysts are the most widely used fuel electrode materials for SOCs due to the low price and high activity.However,when hydrocarbon fuels are employed,nickel-based electrodes face serious carbon deposition challenges,leading to a rapid decline of cell performance.Great efforts have been devoted to understanding the occurrence of the coking reaction,and to improving the stability of the electrodes in hydrocarbon fuels.In this review,we summarize recent research progress of utilizing surface modification to improve the stability and activity of Ni-based electrodes for SOCs by preventing carbon coking.The review starts with a briefly introduction about the reaction mechanism of carbon deposition,followed by listing several surface modification technologies and their working principles.Then we introduce representative works using surface modification strategies to prevent carbon coking on Ni-based electrodes.Finally,we highlight future direction of improving electrode catalytic activity and anti-coking performance through surface engineering.

磷掺杂剂和石墨烯包覆层对NiCo_(2)S_(4)电催化剂析氢活性和耐久性的协同影响

探索具有优异导电性和稳定性的非贵金属电催化剂对氢经济至关重要.本研究将杂原子掺杂和石墨烯包覆相结合,以控制NiCo_(2)S_(4)(NCS)蛋黄壳微球的电子性能,并抵抗酸性介质中H_(2)O和O_(2)的腐蚀.密度泛函理论(DFT)模拟结合综合表征和实验首次揭示了在NCS中引入P杂原子不仅加速了电子从体相向表面的转移动力学,而且降低了掺杂P原子附近活性S位上的析氢反应势垒.利用DFT计算的穿透能垒预测了rGO覆盖层在P掺杂NCS(P-NCS)表面对质子的渗透性和对H_(2)O和O_(2)分子的抵抗性等重要功能,并用X射线光电子能谱对新催化剂和回收催化剂进行了验证.利用P掺杂剂和rGO覆盖层分别辅助电荷传递和质子传递,通过二者的协同作用获得了催化活性和耐久性之间的平衡.因此,优化后的P-NCS/rGO在70 mV的低过电位下实现了10 mA cm^(-2)的电流密度,并具有令人满意的80小时耐用性.本工作阐明了石墨烯覆盖硫化物催化剂可通过调控电子结构和质子/分子穿透提高电催化性能.

New two-layer Ruddlesden-Popper cathode materials for protonic ceramics fuel cells

New two-layer Ruddlesden-Popper(RP)oxide La_(0.25)Sr_(2.75)FeNiO_(7-δ)(LSFN)in the combination of Sr_(3)Fe_(2)O_(7-δ) and La_(3)Ni_(2)O_(7-δ) was successfully synthesized and studied as the potential active single-phase and composite cathode for protonic ceramics fuel cells(PCFCs).LSFN with the tetragonal symmetrical structure(IMmmm)is confinned,and the co-existence of Fe^(3+)/Fe^(4+) and Ni^(3+)/Ni^(2+) couples is demonstrated by X-ray photoelectron spectrometer(XPS)analysis.The LSFN conductivity is apparently enhanced after Ni doping in Fe-site,and nearly three times those of Sr_(3)Fe_(2)O_(7-δ),which is directly related to the carrier concentration and conductor mechanism.Importantly,anode supported PCFCs using LSFN-BaZr_(0.1)Ce_(0.7)Y_(0.2)O_(3-δ)(LSFN-BZCY)composite cathode achieved high power density(426 mW·cm^(-2) at 650℃)and low electrode interface polarization resistance(0.26Ω·cm^(2)).Besides,distribution of relaxation time(DRT)function technology was further used to analyse the electrode polarization processes.The observed three peaks(Pl,P2,and P3)separated by DRT shifted to the high frequency region with the decreasing temperature,suggesting that the charge transfer at the electrode-electrolyte interfaces becomes more difficult at reduced temperatures.Preliminary results demonstrate that new two-layer RP phase LSFN can be a promising cathode candidate for PCFCs.

Robust Joule-heating ceramic reactors for catalytic CO oxidation

Joule-heating reactors have the higher energy efficiency and product selectivity compared with the reactors based on radiative heating.Current Joule-heating reactors are constructed with electrically-conductive metals or carbon materials,and therefore suffer from stability issue due to the presence of corrosive or oxidizing gases during high-temperature reactions.In this study,chemicallystable and electrically-conductive(La_(0.80)Sr_(0.20))_(0.95)FeO_(3)(LSF)/Gd_(0.1)Ce_(0.9)O_(2)(GDC)ceramics have been used to construct Joule-heating reactors for the first time.Taking the advantage of the resistance decrease of the ceramic reactors with temperature increase,the ceramic reactors heated under current control mode achieved the automatic adjustment of heating to stabilize reactor temperatures.In addition,the electrical resistance of LSF/GDC reactors can be tuned by the content of the highconductive LSF in composite ceramics and ceramic density via sintering temperature,which offers flexibility to control reactor temperatures.The ceramic reactors with dendritic channels(less than 100μm in diameter)showed the catalytic activity for CO oxidation,which was further improved by coating efficient MnO_(2)nanocatalyst on reactor channel wall.The Joule-heating ceramic reactors achieved complete CO oxidation at a low temperature of 165℃.Therefore,robust ceramic reactors have successfully demonstrated effective Joule heating for CO oxidation,which are potentially applied in other high-temperature catalytic reactions.