A low crystallinity tungsten supported palladium catalyst and its electrochemical hydrogen evolution activity

Abstract

As one of the most important green hydrogen production technologies, the research on electrochemical hydrogen evolution reaction (HER) catalysts has received widespread attention. Pd, as an important hydrogen storage material, has a strong affinity with H and can enter the Pd lattice to form hydrides. However, this strong hydrogen binding limits the HER process catalyzed by Pd, and its HER activity is 30-40 times lower than that of Pt. Therefore, it is necessary to improve the adsorption characteristics of Pd for H, in order to make it more favorable for the HER process. In this article, a low crystallinity W supported Pd catalyst (Pd@LC-W/Ti) was constructed using the high vacuum magnetron sputtering combined with the liquid-phase reduction method. The surface of the LC-W support is rich in hydroxyl groups, which is conducive to the formation of Pd-O-W structure. This structure can alter the electronic structure of Pd, leading to the formation of Pd2+, which is beneficial for weakening the Pd-H binding energy. The analysis of cyclic voltammetry (CV) curve has clearly confirmed the negative shift of H desorption (Hdes) peak (0.176 V for Pd@LC-W/Ti and 0.226 V for Pd@Ti), which is beneficial to hydrogen desorption. Meanwhile, in the linear sweep voltammetry (LSV) curve, the positive shift of the reduction peak (26 mV for Pd@LC-W/Ti and -24 mV for Pd@Ti) also reflects that the adsorbed H (Hads) is prone to desorb, instead of forming Pd hydride. The analysis of H adsorption charge indicates that Pd@LC-W/Ti (0.229 mC cm-2) can adsorb more H than Pd@Ti (0.162 mC cm-2), which is also one of the reasons for improving HER activity. For Pd@Ti electrode, its HER activity is not ideal, and the overpotential corresponding to the current density of 10 mA cm-2 (η10) is 81 mV. For the Pd@LC-W/Ti electrode, its HER activity was significantly improved, with η10 reduced to 45 mV, which is similar to the HER activity of Pt/C (33 mV). The mechanism of HER on Pd@LC-W/Ti electrode is consistent with the Volmer−Heyrovsky pathway, and the Heyrovsky step (electrochemical desorption) is a rate-determining step (RDS).