Direct formic acid fuel cell (DFAFC) has been considered as a promising power source owing to their high energy density, low toxicity, low operating temperature, and low crossover through the membrane. For the anode catalyst, typically Pt has been used for formic acid oxidation reaction (FAOR). On the Pt surface, the FAOR occurs through the dual-path mechanism, consisting of the dehydrogenation (direct) and dehydration (indirect) pathways. In the dehydrogenation pathway, HCOO_ads is the reactive intermediate and it further oxidized to CO₂. By contrast, in the dehydration pathway, formic acid (FA) is firstly oxidized to intermediate CO_ads and it further reacts with H₂O to produce CO₂. Pt catalyst is susceptible to CO poisoning through dehydration (indirect) pathway, which lowering the overall kinetics for FAOR. To promote the dehydrogenation (direct) pathway, various studies on Pt based binary alloy catalyst have been reported such as Pt-Au, Pt-Pd, Pt-Ag, and Pt-Ru. Among them, the Pt-Au alloy catalysts showed the high selectivity owing to the ensemble effect. However, the alloy catalyst has demerit of low Pt mass activity due to the buried Pt active sites. To solve this problem, many efforts have been conducted to synthesis the Pt-decorated Au catalyst.

In this study, multiple electrochemical steps were employed to prepare high-performance Pt-decorated Au dendrite catalyst for DFAFC. At first, Ni film was electrodeposited on carbon paper (CP). After Au displacement and subsequent electrochemical etching, porous Au dendrite was prepared on CP (Au/CP). Then, Pt self-terminated electrodeposition (SED) was performed on Au/CP. SED facilitates the atomic layer deposition of Pt via repeated deposition pulses on Au substrate. By applying the highly negative potential Pt deposition is quenched by immediate H adsorption, which prevent the further Pt deposition. The H passivated Pt surfaces are reactivated with applying the positive potential for oxidation of the adsorbed H. By controlling the number of deposition pulse, Pt loading mass, Pt roughness, and Pt coverage on Au can be easily controlled. The Pt loading mass and Pt coverage of Pt1/Au/CP were 0.005 mg_Pt/cm² and 0.45, respectively. The FAOR performance of the prepared Pt/Au/CP was measured by cyclic voltammetry (CV). During the CV test, an enhancement of the selectivity for direct pathway is observed in all electrodes. The density functional theory calculation revealed that this unexpected enhancement is due to the decreased Pt coverage during the FAOR. The 20 cycled Pt1/Au/CP exhibited the high selectivity for the direct pathway of FAOR, and extremely higher mass activity compared with state-of-the-art Pt-Au catalyst. The CO chemisorption measurement using in-situ diffuse reflectance infrared Fourier transform spectroscopy spectra confirmed that a few Pt atoms were formed on Au/CP and their stability during the FAOR. Finally, the prepared electrode was employed for the anode of DFAFC single-cell tests, exhibiting superior Pt mass activity than state-of-the-art Pt–Au catalysts.