Regulation of the Work Function Difference Promotes In Situ Phase Transition of WO 3- x for Efficient Formate Electrooxidation.

Direct formate fuel cells (DFFCs) have drawn tremendous attention because they are environmentally benign and have good safety. However, the lack of advanced catalysts for formate electrooxidation hinders the development and applications of DFFCs. Herein, we report a strategy of regulating the metal-substrate work function difference to effectively promote the transfer of adsorbed hydrogen (H _ad ), thus enhancing formate electrooxidation in alkaline solutions. By introducing rich oxygen vacancies, the obtained catalysts of Pd/WO _{3- x} -R show outstanding formate electrooxidation activity, exhibiting an extremely high peak current of 15.50 mA cm ^-2 with a lower peak potential of 0.63 V. In situ electrochemical Fourier transform infrared and in situ Raman measurements verify an enhanced in situ phase transition from WO _{3- x} to H _x WO _{3- x} during the formate oxidation reaction process over the Pd/WO _{3- x} -R catalyst. The results of experimental and density functional theory (DFT) calculations confirm that the work function difference (ΔΦ) between the metal (Pd) and substrate (WO _{3- x} ) would be regulated by inducing oxygen vacancies in the substrate, resulting in improved hydrogen spillover at the interface of the catalyst, which is essentially responsible for the observed high performance of formate oxidation. Our findings provide a novel strategy of rationally designing efficient formate electrooxidation catalysts.