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The homogeneous/heterogeneous catalyst combination of VO2+ in anolyte with Pd/C at the anode is first introduced in a formic acid fuel cell to enhance HCOOH electrooxidation. The VO2+/Pd catalyst combination establishes a stepwise reaction pathway involving HCOOH dehydrogenation to form V3+ from VO2+ reduction and subsequent V3+ electrooxidation to regain VO2+. The fuel cell with the VO2+/Pd combination presents a peak power density of 341.3 mW cm−2 and stable power density higher than 30 mW cm−2. [ABSTRACT FROM AUTHOR]

• Poor hydrocarbon diffusion against CO 2 evolution leads to poor anode performance in DLFCs. • Reaction-separation anode features distinct pathways for hydrocarbon diffusion and CO 2 release. • CO 2 pathway is built by the hydrophobic catalyst layer and gas diffusion layer. • Hydrocarbon pathway is built by the hydrophilic catalyst layer and liquid diffusion layer. • The FAFC with the reaction-separation anode presents a power density as high as 433.5 mW cm−2. Direct liquid-feed fuel cells (DLFCs) have been considered as a potential power candidate for portable electronic devices and electric vehicles. However, evolution of CO 2 arising from hydrocarbon electrooxidation leads to a great diffusion resistance of hydrocarbon in anode, seriously retarding the anode process of DLFCs. Herein, this work suggests a reaction-separation anode to separate gaseous CO 2 from liquid anolyte to decrease polarization, using the formic acid fuel cell (FAFC) as an example of the DLFCs. The reaction-separation anode is composed of hydrophilic and hydrophobic components. The hydrophilic component includes a Nafion-based catalyst layer and a liquid diffusion layer contacting to the membrane. The hydrophobic component includes a poly(tetrafluoroethylene)-based catalyst layer and a gas diffusion layer contacting to the flow-field of anode plate. The hydrophilic component provides the anolyte diffusion pathway while the hydrophobic component enhances the CO 2 release. Such a reaction-separation anode with configuration of the liquid-diffusion-layer/hydrophilic-catalyst-layer/hydrophobic-catalyst-layer/gas-diffusion-layer shows small polarization, presenting excellent anode performance. A power density as high as 433.5 mW cm−2 is achieved when using a vanadyl sulfate-contained formic acid anolyte as the fuel to run the FAFC with the reaction-separation anode. This innovative anode makes a significant progress in development of FAFC technology, shedding a light on the resolution of the mass transfer difficulty in the anode of DLFCs. [Display omitted] [ABSTRACT FROM AUTHOR]