Electrochemical Proton Insertion Modulates the Hydrogen Evolution Reaction on Tungsten Oxides

Development of new electrocatalysts for the hydrogen evolution reaction (HER) could reduce dependence on Pt and other rare metals and enable large-scale production of hydrogen with near-zero carbon emissions. Mechanistic insight into the electrocatalytic activity of a material helps to accelerate the development of new electrocatalysts. Alternative electrocatalyst materials such as transition metal oxides and sulfides can undergo insertion reactions that change their properties. Recent reports indicate that the presence of inserted ions can influence electrocatalytic activity. Here, we utilized a materials chemistry approach to understand the role of proton insertion on the HER activity of layered tungsten oxide hydrates (WO3∙xH2O, x = 1, 2). We synthesized a series of tungsten oxide hydrates along with an octylamine-pillared tungsten oxide (OA-WO3). We used cyclic voltammetry to study the electrochemical reactivity of each material and performed ex situ X-ray diffraction and Raman spectroscopy to understand bulk and surface structural changes during electrochemical cycling. We show an inverse relationship between the degree of proton insertion and HER overpotential in tungsten oxides: the lack of proton insertion leads to a high overpotential for the HER. We discuss three hypotheses for how proton insertion leads to HER activity in WO3∙xH2O: 1) proton insertion changes the electronic band structure of WO3∙xH2O, 2) the presence of bulk protons can influence at the surface sites, and 3) inserted protons may participate in the HER mechanism on WO3∙xH2O. Overall, this work shows the critical role of proton insertion in enabling high HER activity in tungsten oxides.The authors would like to thank Dr. Fred Stevie for assisting with XPS measurements and Sarah Morgan for acquiring N2 adsorption isotherms. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Early Career Research Program under Award Number DE-SC0020234. This work was performed in part at the Analytical Instrumentation Facility (AIF) at North Carolina State University, which is supported by the State of North Carolina and the National Science Foundation (award # ECCS-2025064). The AIF is a member of the North Carolina Research Triangle Nanotechnology Network (RTNN), a site in the National Nanotechnology Coordinated Infrastructure (NNCI)