Oxygen Vacancy-rich 1D In-doped SnO₂ Hollow Nanofibers As An Efficient CO₂ Electroreduction Catalyst

Global net human-caused emissions of carbon dioxide?CO₂?,which is one of the chief culprits of climate warming,would need to fall imperatively.Therefore,measures should be taken to deal with the overwhelming CO₂ problem.The electrochemical reduction of CO₂?CO₂ER?closes the carbon cycle and the greenhouse gas will be converted into value-added chemicals.The strategy of further cooperated with intermittent renewable energy storage technology tackles both CO₂ emissions mitigation as well as renewable energy storage.Electrochemical hydrogen pump reactor?EHPR?with a circulating buffer layer has been applied to conduct the CO₂ER in this work.In EHPR,mass transfer resistance could be reduced due to the direct CO₂ feeding to the cathodic active sites and the extremely thin buffer layer.However,most recent studies of EHPR mainly focus on the reactor configuration rather than catalysts,the lack of an active catalyst designed to match the three-phase reaction interface limits their hydrogenation performance.Therefore,highly active and selective catalysts are in great demand to electrochemically convert CO₂ into value-added chemicals.Here in this work,the manipulation of catalyst morphology,together with the fine tuning of electronic densities are integrated to upgrade the catalytic behavior.A one-dimensional hollow nanofiber tin-based catalyst is developed by electrospinning technique for the purpose of providing high surface area and facilitating directional charge and mass transfer.And the annealing process is more likely to form grain boundaries,ie,plain defects,which improve the catalytic active sites.In addition,In-doping strategy was conducted to further enhance the catalytic activity.The formed In₂O₃ nanocrystallites act as grain growth inhibitors to effectively suppress the SnO₂grain size and further enlarge the surface area.And the electronegativity gradient of these two different elements promote the increase of the electron density on Sn,which enhances the conductivity of SnO₂ as a n-type semiconductor.Finally,oxygen vacancies are introduced on the surface via a facile in-situ electrochemical prereduction method,and have been proved by the characterization test of XPS and EPR.Oxygen vacancies could increase the reaction selectivity towards HCOOH by stabilizing the CO₂^·-intermediate in an O-bound manner.This mechanism meanwhile gives insight into the significantly enhanced performance of“oxide derived”metal.The excellent overall performance of the oxygen vacancy-rich one dimensional In-doped SnO₂ hollow nanofiber catalyst is attained.Especially,considerable HCOOH partial current density of about 28.5 mA cm^-2,high faradaic efficiency of about 86.2%with 532.3?mol h^-1cm^-2 formation rate are achieved at-1.34 V?vs.RHE?.The performance is within the first level reported in the literature.