表面氧物种调控提升钙钛矿电化学甲烷氧化偶联性能OA

Ethylene,essential for chemical intermediates and polymers,faces sustainability challenges in production.Conventional steam cracking achieves more than 90%thermal efficiency but emits 1-2 t CO2 per ton of ethylene.Thermochemical oxidative coupling of methane offers an alternative yet struggles with methane activation,over-oxidation,low oxygen efficiency,and safety risks.Solid oxide electrolysis cells(SOECs)present advantages:they utilize renewable electricity to drive electrochemical oxidative coupling of methane(E-OCM)with separated methane(anode)and oxidant(cathode)feeds,eliminating direct mixing.CO2 or H2O can serve as oxidants,which potentially enables carbon-negative operation when CO2 is used.However,as anode materials of SOECs,lanthanum strontium manganate(LSMO)synthesized by the solid-state or sol-gel method often lacks controlled morphology,which results in surface oxygen species dictated by random crystal facets.This compromises selectivity for ethylene production in E-OCM.LSMO was synthesized by the molten salt synthesis method(LSMO-MS).XRD and TEM were used to analyze its crystal structure,revealing the same rhombohedral R-3C space group as that of LSMO prepared by the sol-gel method(LSMO-SG).SEM characterization shows a cubic morphology.Further XPS peak analysis of the O 1s spectrum indicates that the atomic ratio of surface adsorbed oxygen to lattice oxygen in LSMO-MS(0.71)is lower than that in LSMO-SG(0.98),which is good for selectivity of C2+production.During LSMO-SG synthesis,CO2 generated from organic combustion reacts to form additional carbonate secondary phases on the oxide surface.It will decompose to create isolated SrO islands at high temperatures,which increase the material's electrochemical impedance and degrade its electrochemical performance.Electrochemical testing demonstrates that LSMO-MS electrolytic cell plate exhibits a lower electrolysis potential for the electrochemical CO2 reduction reaction coupling with E-OCM.The electrolysis potential is reduced by more than 0.6 V at 100 mA/cm2,significantly lowering the energy consumption of the reaction.Concurrently,the selectivity of C2+products in this reaction increases,reaching 67.4%at 200 mA/cm2.The analysis of reaction products at different methane concentrations confirms the competitive relationship between oxidative coupling of methane and deep oxidation.High methane concentration suppresses deep oxidation by reducing adsorption of reaction products on the electrode surface,enabling direct methane reaction with oxygen ions and decreasing r eactive oxygen concentration.This study demonstrates that the molten salt synthesis method can modulate the surface oxygen species of perovskite oxides,thereby optimizing their catalytic performance for the E-OCM reaction.It represents an effective strategy for enhancing E-OCM materials in SOECs.