A Study of the Mechanism of the Hydrogen Evolution Reaction on Nickel by Surface Interrogation Scanning Electrochemical Microscopy

Abstract

The hydrogen evolution reaction (HER) on Ni in alkaline media was investigated by scanning electrochemical microscopy under two operating modes. First, the substrate generation/tip collection mode was employed to extract the "true" cathodic current associated with the HER from the total current in the polarization curve. Compared to metallic Ni, the electrocatalytic activity of the HER is improved in the presence of the low-valence-state oxide of Ni. This result is in agreement with a previous claim that the dissociative adsorption of water can be enhanced at the Ni/Ni oxide interface. Second, the surface-interrogation scanning electrochemical microscopy (SI-SECM) mode was used to directly measure the coverage of the adsorbed hydrogen on Ni at given potentials. Simulation indicates that the hydrogen coverage follows a Frumkin isotherm with respect to the applied potential. On the basis of the combined analysis of the Tafel slope and surface hydrogen coverage, the rate-determining step is suggested to be the adsorption of hydrogen (Volmer step) in the investigated potential window.

In situ fabricated nickel vanadate/N-doped reduced graphene oxide hybrid as an advanced electrocatalyst in alkaline hydrogen evolution reaction

“…35,51 This could be facilitated by adding another active component on the surface of NV/NRGO2 to achieve similar/better HER activity to/than that of Pt/C in an alkaline medium. [52][53][54] In summary, an Ni 3 V 2 O 8 /NRGO hybrid with 5.6 wt% NRGO content was successfully fabricated through reuxing and employed as an electrocatalyst for HER in an alkaline medium (1.0 M KOH). The superior performance of the Ni 3 V 2 O 8 /NRGO (5.6 wt%) hybrid manifested a very low overpotential ($43 mV), small Tafel slope ($54.8 mV dec À1 ), and quite high exchange current density ($1.24 mA cm À2 ) for hydrogen evolution in 1.0 M KOH.…”

Bottom-up Synthesis of Porous NiMo Alloy for Hydrogen Evolution Reaction

“…Therefore, the Heyrovsky desorption process (H 2 O + e − + H* → H 2 + OH − ), where H* represents adsorbed H atom on catalytic site *) could be the rate determining step for the NiMo-950 • C in 1 M KOH electrolyte [26]. The Tafel slopes of NiMo-900 • C and NiMo-800 • C are 72 mV/decade and 147 mV/decade, indicating the mixed Volmer-Heyrovsky process (H 2 O + e − + H* → H 2 + OH − and H 2 O + e − → H* + OH − ) are the corresponding rate determining steps [27,28]. The EIS measurements were further carried out to measure the charge-transfer resistances (R ct ) of the porous NiMo alloys at an overpotential of 200 mV vs. RHE (Figure 4c).…”

Direct Observation of Ni–Mo Catalyst Formation via Thermal Reduction of Nickel Molybdate Nanorods

“…Indeed, numerous recent reports have emerged indicating that alkaline HER electrocatalysts based on precious and nonprecious metals benefit from synergistic interactions between metallic and oxidized surface sites. [74][75][76][77][78] We speculate that the active catalytic unit in these Ni-Mo composites may in fact be interfacial sites where Ni, MoO x , and aqueous electrolyte coexist under HER reaction conditions. Accordingly, the decrease in activity at reduction temperatures above 400 • C would then be attributable to a significant decrease in metal-oxide contact area associated with sintering and consolidation of larger nanoparticles.…”