Electrochemical proton insertion modulates the hydrogen evolution reaction on tungsten oxides

Abstract

The development of new electrocatalysts for the hydrogen evolution reaction (HER) could reduce the 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 the electrocatalytic activity. Here, we utilized a materials chemistry approach to understand the role of proton insertion in the HER activity of the 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 the HER activity in WO3·xH2O: (1) proton insertion changes the electronic band structure of WO3·xH2O, (2) the presence of bulk protons can influence ΔGH,ads at the surface sites, and (3) the inserted protons may participate in the HER mechanism on WO3·xH2O. Overall, this work shows the critical role of proton insertion in enabling the high HER activity in tungsten oxides.

Impact of Reversible Proton Insertion on the Electrochemistry of Electrode Materials Operating in Mild Aqueous Electrolytes: A Case Study with TiO2

“…[ 27 ] More recently, the Augustyn and Mpourmpakis/McKone groups have both suggested that protons inserted into WO 3 govern the reactivity toward the hydrogen evolution reaction. [ 28,29 ] All these elements reinforce the idea that there is a crucial need to elucidate the key factors governing PICET reactions, and more specifically in aqueous unbuffered media. This is of prime interest for the development/optimization of not only water‐based electrochemical charge storage devices, but also of many water‐based energy conversion systems.…”

Choice of Electrolyte Impacts the Selectivity of Proton-Coupled Electrochemical Reactions on Hydrogen Titanate

“…Protons have a smaller mass and volume as compared to other cations (H + mass ∼ 1.67 × 10 –15 ng, ionic radius ∼ 10 –5 Å; H 3 O + ionic size = 2.82 Å) and can also undergo hydrogen bonding . Reports show that protons are the predominant insertion species in mildly acidic electrolytes, necessitating the re-evaluation of cation insertion from aqueous electrolytes into TMOs. , Previous work by our group, as well as Miu et al, showed that PCET processes on TMOs can be coupled to HER, whereby proton insertion into tungsten oxides influences their HER activity. , Another report showed the importance of PCET reactions for facilitating high-energy oxidation reactions in multimetallic catalysts by circumventing the high-energy intermediates that form through stepwise reactions . Here, we aim to understand the role of electrolyte on PCET mechanisms in an important class of TMOs for aqueous energy applicationsthe titanium oxides.…”

“…8,9 Previous work by our group, as well as Miu et al, showed that PCET processes on TMOs can be coupled to HER, whereby proton insertion into tungsten oxides influences their HER activity. 10,11 Another report showed the importance of PCET reactions for facilitating high-energy oxidation reactions in multimetallic catalysts by circumventing the high-energy intermediates that form through stepwise reactions. 12 Here, we aim to understand the role of electrolyte on PCET mechanisms in an important class of TMOs for aqueous energy applications�the titanium oxides.…”

Mechanistic understanding of microstructure formation during synthesis of metal oxide/carbon nanocomposites

“…In particular, we aim to answer whether a heterostructured microstructure forms, where in an ideal case, 2D The reaction mechanism of alkylamines with molybdic acids can be likened to that in isostructural tungstic acids, which has been described in literature to occur via a dissolution-reorganization mechanism that leads to a change in the morphology and particle size. 28,29 Scanning electron micrographs of MoO 3 -$2H 2 O and MoO x -OA (Fig. 1B and C) show an increased particle size aer reaction with octylamine.…”