Si regulation of hydrogen adsorption on nanoporous PdSi hybrids towards enhancing electrochemical hydrogen evolution activity

Abstract

Electrocatalytic water splitting to produce hydrogen is a zero-carbon emission process, which has a wide application prospect. At present, platinum (Pt) is undoubtedly the best catalyst for the hydrogen evolution reaction (HER) in an acidic solution. Pd has attracted attention as a substitute catalyst for Pt, but there are still some key problems to be solved. The strong hydrogen affinity of Pd is not conducive to the desorption of adsorbed hydrogen, which limits its HER activity. In this study, silicon (Si), as a light atom, is used for the first time to regulate the adsorption of hydrogen on the surface of Pd, thus improving the activity of HER. In order to realize the systematic, accurate and controllable preparation of nanoporous PdSi (NP-PdSi) hybrids, a series of NP-PdSi hybrids with different Si contents were prepared by advanced high vacuum magnetron sputtering technology. The addition of Si enables the special morphology of a porous structure, and the increased Si content will gradually reduce the grain size of the NP-PdSi hybrids. The most important aspect is that the Si content is closely related to the hydrogen adsorption and desorption potential of the NP-PdSi hybrids. The addition of Si can obviously change the electronic structure and hydrogen adsorption energy of Pd, thus bringing excellent HER activity to the NP-PdSi hybrids. Among them, the HER activity of the Pd₃Si catalyst is the best. Its overpotential is 16.5 mV at the current density of 10 mA cm⁻² (η₁₀) and the Tafel slope is 27.7 mV dec⁻¹, which not only significantly exceeds Pd, but also exceeds Pt/C. The ΔG_H of Pd₃Si is closer to 0 than that of Pt, which indicates that Pd₃Si is more suitable to adsorb and activate hydrogen atoms. Moreover, the electrochemical hydrogen evolution mechanism on the surface of the Pd₃Si catalyst is obviously different from that on the surface of Pd. The HER mechanism of Pd₃Si can be described as a Volmer–Tafel mechanism (Tafel step is the rate-determining step), which is the same as that of Pt.