Anomalous hydrogen evolution behavior in high-pH environment induced by locally generated hydronium ions

Abstract

Most fundamental studies of electrocatalysis are based on the experimental and simulation results obtained for bulk model materials. Some of these mechanistic understandings are inapplicable for more active nanostructured electrocatalysts. Herein, considering the simplest and most typical electrocatalytic process, the hydrogen evolution reaction, an alternative reaction mechanism is proposed for nanomaterials based on the identification of a new intermediate, which differs from those commonly known for the bulk counterparts. In-situ Raman spectroscopy and electrochemical thermal/kinetic measurements were conducted on a series of nanomaterials under different conditions. In high-pH electrolytes with negligible hydronium (H3O+) concentration in bulk phase, massive H3O+ intermediates are found generating on the catalytic surface during water dissociation and hydrogen adsorption processes. These H3O+ intermediates create a unique acid-like local reaction environment on nanostructured catalytic surfaces and cut the energy barrier of the overall reaction. Such phenomena on nanostructured electrocatalysts explain their widely observed anomalously high activity under high-pH conditions.

Identifying the Transfer Kinetics of Adsorbed Hydroxyl as a Descriptor of Alkaline Hydrogen Evolution Reaction

“…% Pt) catalysts in different concentrations of KOH all follow the same order: 1m KOH > 0.1m KOH @ 0.01m KOH (Figure 3 d and Figure S23), in good agreement with the activity trend of nanostructured HER catalysts reported previously. [19] These results further confirm a direct correlation between the surface charge and the activity of the catalyst. As a consequence, it can be inferred that the higher negative charge density on nanostructured catalysts may be more conducive to the desorption of OH adtransferred OH À in alkaline media, thereby effectively promoting the transfer kinetics of OH ad + e À Q OH À .…”

Perspective on experimental evaluation of adsorption energies at solid/liquid interfaces

“…Important to emphasize is that observed trend could be distorted due to appearance of H u pd (underpotentially deposited hydrogen). Our initial point of view was that under neutral pH conditions of our experiment (hydrogen introduced through the thin water layer) H upd is not significant as shown in the work of Qiao et al [37]. However, on the contrary, under neutral pH conditions and very clean experimental conditions, H upd exists on platinum [38], implying that under our measurement conditions, H upd exists and it could interfere with the adsorption of atomic hydrogen originating from the hydrogen gas.…”

Operando Unraveling Photothermal-Promoted Dynamic Active Sites Generation in Spinel NiFe2O4 for Oxygen Evolution

“…To further uncover the mechanism of photothermal effect on promoting the catalytic activity of NFO/NF during OER process, the activation energy E a at the zero overpotential (η = 0) was calculated, which is widely regarded as an important descriptor for evaluating the performance of electrocatalysis. [21] Derived from the LSV curves in Fig. 4c (for example, reading the current densities j at different temperatures for a given overpotential), the Arrhenius plots displayed the semilogarithmic dependences of j on the inverse temperature (see Experimental Section), [22] that is, a linear relationship at varied overpotentials (Fig.…”