Enhancing Formic Acid Electrooxidation Selectivity on Pd via Promoting Interfacial Charge Transfer by Polarization-Induced Electric Field

Direct formic acid fuel cells (DFAFCs) are promising portable power sources with the advantages of easy handling and high theoretical open-circuit voltage. Exploring efficient Pd-based catalysts for formic acid oxidation (FAO) on the anode is important for the widespread use of DFAFCs. However, formic acid decomposition on the Pd surface restricts the FAO activity of the catalyst, in which the adsorbed hydrogen atoms combine together to form hydrogen molecules instead of generating H+ ions and transferring electrons at the interface. Herein, we report a polarization-induced electric field (PEF) strategy to facilitate FAO on Pd by directing interfacial charge transfer. Pd/TBT-X@SC catalysts with PEF are synthesized with tetragonal phase barium titanate (TBT) as the core, carbonized sucrose as the shell, and palladium nanoparticles as the active sites. The PEF strength is successfully regulated by varying the particle size of TBT. Stronger PEF and proper carbonized sucrose thickness facilitate the interfacial charge transfer on the Pd surface, thereby promoting the electrooxidation of adsorbed hydrogen to H+ ions and converting CO-like species to CO2. Moreover, PEF also induces the formation of electron-deficient Pd, thus reducing the bond strength between Pd and adsorbed intermediate species such as H and CO-like species. Consequently, FAO selectivity, activity, and anti-CO-like poisoning species property of Pd are enhanced by the introduction of PEF. Among all the catalysts, Pd/TBT-100 nm@SC exhibits the highest catalytic activity (7.49 mA·cm–2) and resistance to CO-like poisoning species. This work offers a new strategy for the design of catalysts with high FAO selectivity.