Donor-Dependent Promotion of Interfacial Proton-Coupled Electron Transfer in Aqueous Electrocatalysis

Abstract

Efficient interfacial electrocatalysis requires rapid concerted proton−electron transfer (CPET) at the electrode surface, a process for which there is little mechanistic understanding. In aqueous media, multiple proton donors coexist, adding to the mechanistic complexity. Herein, we examine the rate of the hydrogen evolution reaction (HER) on Au, a proxy for CPET to Au, as a function of the concentration of exogenous phosphate and borate proton donors. We find that the reaction order in phosphate is 0.6, whereas the reaction order in borate is close to 0, indicating that phosphate, unlike borate, can outcompete water as a proton donor for interfacial CPET. Promotion in phosphate is substantial; the rate of the HER on Au in saturated potassium phosphate at pH 6.8 is identical to the rate of the HER on Au at pH 1. Additionally, we demonstrate that buffer-promoted CPET is a phenomenon that extends beyond Au to an Earth-abundant catalyst, NiS x . Kinetic data indicate that interfacial CPET cannot be viewed as a simple bimolecular reaction between the donor and a surface site, but that it first requires the formation of a preassociation complex embedded in the double layer. Our results emphasize that both the proton donor and the donor's environment control the rate of interfacial CPET and consequently have profound effects on the rate of heterogeneous electrocatalysis.

Electrolyte Effects on the Electrochemical Reduction of CO2

“…Therefore, using anions with a low buffering capacity will result in a suppression of H 2 and CH 4 production. This hypothesis is supported by recent work of Jackson et al., that shows that phosphate can outcompete water as a proton donor in the hydrogen evolution reaction on a gold electrode …”

“…This hypothesis is supported by recent work of Jackson et al, that shows that phosphate can outcompete water as a proton donor in the hydrogen evolution reaction on a gold electrode. [61]…”

Switching of Kinetically Relevant Reactants for the Aqueous Cathodic Process Determined by Mass‐transport Coupled with Protolysis

“…In fact, in many studies, the proton released by the buffering action (or, the protolysis) is considered to directly participate in elementary steps of both the HER and CO 2 reduction. [19,20,22] Looking at the system from a different angle, one can consider that such buffering ions may directly interact with the catalytically active site, in which the direct reduction of the proton-containing species evidences the HER [Equation (6)]: [21,[23][24][25][26][27] 2HA þ 2e À ! H 2 þ 2A À :…”

Devisable POM/Ni Foam Composite: Precisely Control Synthesis toward Enhanced Hydrogen Evolution Reaction at High pH

“…One of the most promising routes to generate hydrogen is electrochemical water splitting. The hydrogen evolution reaction (HER) reaction is a typical two‐electron transfer reaction, and involves interfacial proton‐coupled electron transfer and concomitant hydrogen evolution . Compared with the electrolysis process in acidic media, HER in alkaline electrolysis is more favourable for electrochemical water splitting due to the robustness of electrode materials, long lifetime of catalysts, cheap electrolyser construction and less equipment corrosion .…”

“…The hydrogen evolution reaction (HER) reaction is at ypical two-electron transfer reaction, and involves interfacial proton-coupled electron transfer and concomitant hydrogen evolution. [3][4][5] Compared with the electrolysis process in acidic media, HER in alkaline electrolysis is more favourable for electrochemical water splitting due to the robustness of electrode materials, long lifetime of catalysts, cheap electrolyser construction and less equipment corrosion. [6][7][8] However, HER reactionr ate for most catalysts in alkalines olution is 2-3 orders of magnitude lower than that in acidic solution, [9,10] and HER application is largelyl imited by sluggish kinetics in alkaline solution.…”