Improving the hydrogen oxidation reaction rate by promotion of hydroxyl adsorption

Abstract

The development of hydrogen-based energy sources as viable alternatives to fossil-fuel technologies has revolutionized clean energy production using fuel cells. However, to date, the slow rate of the hydrogen oxidation reaction (HOR) in alkaline environments has hindered advances in alkaline fuel cell systems. Here, we address this by studying the trends in the activity of the HOR in alkaline environments. We demonstrate that it can be enhanced more than fivefold compared to state-of-the-art platinum catalysts. The maximum activity is found for materials (Ir and Pt₀.₁Ru₀.₉) with an optimal balance between the active sites that are required for the adsorption/dissociation of H₂ and for the adsorption of hydroxyl species (OHad). We propose that the more oxophilic sites on Ir (defects) and PtRu material (Ru atoms) electrodes facilitate the adsorption of OHad species. Those then react with the hydrogen intermediates (Had) that are adsorbed on more noble surface sites.

Towards Versatile and Sustainable Hydrogen Production through Electrocatalytic Water Splitting: Electrolyte Engineering

“…On the other hand, Markovic and co‐workers claimed that a microkinetic description, in conjunction with Fick's law for the HER (hydronium ion reduction and water molecule reduction), and the HOR (hydrogen oxidation with a water molecule and hydroxide ion) matches the experimental observation 118. Similarly to the previous case, the initial reduction events at a lower overpotential and near‐neutral pH are attributed to the diffusion‐limited hydronium ion reduction.…”

“…This section systematically discusses influences of pH on the HER performance. Conventionally, near‐neutral pH conditions have been considered as unfavorable for the electrochemical water splitting reaction, and, until recently, little attention has been paid to these conditions 116, 117, 118. We thus lack a clear fundamental understanding of the reaction under these conditions.…”

“…A systematic study on the influence of pH on the HER was reported by Markovic and co‐workers in 2013 118. In their study, 0.1 mol L −1 KClO 4 (unbuffered) was used as a supporting electrolyte across the entire pH range (pH 1–13), and a single‐crystal Pt (111) electrode was employed as a model electrode.…”

“…In their study, 0.1 mol L −1 KClO 4 (unbuffered) was used as a supporting electrolyte across the entire pH range (pH 1–13), and a single‐crystal Pt (111) electrode was employed as a model electrode. The linear sweep voltammograms (LSVs) are depicted in Figure 6 a on the SHE scale 118. In the figure, in acidic solutions of pH≤2 and at alkaline pH (pH>10), only sharply increasing cathodic currents are obtained.…”

“…The interpretation of the influence of pH on the HER current–potential relationship (Figure 6) is still under debate 116, 117, 118, 119, 120. Mayrhofer and co‐workers reported that the Nernst–Planck equation [Eq.…”