Preparation Of Formate Electrooxidation Catalyst On Modified Pd/WO₃

As the energy structure transforms towards a low-carbon one,the scale of new energy technology is on the increase.In particular,direct alkaline fuel cells（DAFC）have drawn tremendous attention,which use formate as a fuel.However,the performance of direct formate fuel cells（DFFC）is far below the practical demand,which is mainly caused by the slow kinetics of formate oxidation reaction（FOR）on anodic catalysts.Therefore,a grand challenge confronted by DFFC is to develop efficient and robust electrocatalysts for FOR in alkaline electrolytes.Palladium（Pd）based materials are usually considered the most efficient electrocatalysts for FOR in alkaline electrolytes.However,during the FOR,the generated intermediate material adsorbed hydrogen(H_ad)would occupy the active sites of Pd and prevent further adsorption of HCOO^-,thus leading to poor performance of Pd-based electrocatalysts.Therefore,how to efficiently remove H_ad from the surface of Pd-based catalysts and improve the catalytic kinetics of FOR has become an important challenge.Herein,we prepared and modified Pd/WO₃ as efficient catalysts to enhance the FOR performance.（1）Regulating the work function difference（ΔΦ）between metal（Pd）and substrate（WO₃）:Firstly,Pd/WO_3-x-R catalyst was successfully prepared by the sodium borohydride reduction method,then Pd/WO_3-x-R was calcined to obtain the control sample Pd/WO_3-x-P.The results of experiments show that Pd/WO_3-x-R possesses abundant oxygen vacancies（OVs）and theΔΦof the Pd-substrate is decreased.Pd/WO_3-x-R shows a higher peak current and lower oxidation peak potential compared with Pd/WO_3-x-P.In high concentrations of formate solution,Pd/WO_3-x-R exhibits outstanding formate electrooxidation activity.In situ spectroscopic techniques verified an improved hydrogen spillover process occurred at the interface of Pd/WO_3-x-R catalyst,accompanied by an enhanced in-situ phase transition from WO_3-x to H_xWO_3-x during the FOR process.The results of DFT calculations confirm that theΔΦbetween metal（Pd）and substrate(WO_3-x)would be regulated by inducing oxygen vacancies in the substrate,resulting in an improved hydrogen spillover at the interface of catalyst,which is essentially responsible for the observed high performance of formate oxidation.（2）Modulating the d-band center strategy of Pd by ethylene glycol on Pd/WO₃:Pd/WO₃ modified by EG（EG-Pd/WO₃）was prepared.The obtained EG-Pd/WO₃ exhibits excellent activity for FOR,which shows a low potential of 0.25 V with an extremely high peak current of 21.4 m A cm^-2.DFT calculations show that the EG in the EG-Pd/WO₃ catalyst could downshift the d-band center of Pd and weaken the bonding ability of Pd-H,thus reducing the adsorption of H_ad and removing H_ad from Pd.In summary,the designed and prepared Pd/WO_3-x-R and EG-Pd/WO₃catalysts are meaningful for FOR performance improvement in DFFC,which also provides a novel strategy for modifying other noble metal catalysts and applying them to other fields of electrocatalysis.