Understanding the Hydrogen Evolution Reaction Kinetics of Electrodeposited Nickel‐Molybdenum in Acidic, Near‐Neutral, and Alkaline Conditions

Abstract

Nickel‐molybdenum (NiMo) alloys can be a possible alternative to platinum as hydrogen evolution reaction (HER) catalysts because of the superior HER activity. However, the superior HER activity and the pH‐dependent kinetics are not currently fully understood. Herein, we present a study of HER kinetics and mechanisms of NiMo in alkaline, near‐neutral and acidic media by combining voltammetry measurements with electrochemical impedance spectroscopy and a microkinetic model. The results indicate that, compared to Ni, NiMo has significantly higher active surface area and intrinsic HER activity. In the subsequent measurements, we demonstrated that different from the existing explanations to the HER mechanisms for NiMo, the HER process in acidic, near‐neutral, and alkaline media is controlled by the Heyrovsky step. Our results show that increasing pH increases the hydrogen coverage, which increases the Tafel‐slope at low overpotentials, eventually resulting in only a single Tafel slope, which would commonly be interpreted as a Volmer‐limited reaction. Furthermore, the studies of thickness effect on HER kinetics show that the HER kinetics of NiMo are thickness‐dependent. In phosphate buffer, the increase in thickness did not significantly increase the double‐layer capacitance, but simulations with the microkinetic model indicate that the active surface area still increased similarly to other electrolytes, which is likely related to the type of electrolyte used.

Ferroelectric Modulation of Surface Electronic States in BaTiO3 for Enhanced Hydrogen Evolution Activity

“…This suggests slower HER kinetics on the BaTiO 3 surface in comparison with traditional HER electrocatalysts: e.g., metal oxides or noble metals with Tafel slope values of 40–120 mV/dec depending on the governing mechanism. The slow kinetics of the HER and high Tafel slopes for our catalysts may be due to the intrinsic catalytic properties of BaTiO 3 and also the implementation of a near-neutral buffer electrolyte , and are in agreement with limited HER activity and Tafel slopes previously reported for TiO 2 -based catalysts. , …”

One A3B Porphyrin Structure—Three Successful Applications

“…By comparing the results with the voltammogram recorded for the G P2-DMF ( Figure 17 d), it can be concluded that this electrode, manufactured by drop-casting one layer of Pt-porphyrin, displayed the highest HER catalytic activity. Although it is expected for a thicker film to provide a higher active surface area and thus a faster HER kinetics, usually a thicker and compact film that is neither sufficiently porous nor permeable does not determine higher HER activity [ 81 ]. The electroactive surface area (EASA) value of G P2-DMF was estimated using the previously specified Randles–Sevcik equation, together with cyclic voltammetry data from cycles obtained for the electrode in 1 M KNO 3 electrolyte solution, in the absence and in the presence of 4 mM K 3 [Fe(CN) 6 ], at different scan rates (v = 50, 100, 150, 200, 250, 300 and 350 mV/s).…”

Intra-Lattice Inverse Charge Transfer in Bimetallic Electrocatalysts

“…Although reports on the acidic HER activity of Ni-Mo catalysts are scarce, this activity is found comparable with the available literature (Figure S15b). [60][61][62][63][64] Figure 4e demonstrates the excellent durability of Ni73Mo in both alkaline and acidic media. In 1M KOH, the catalyst is stable for at least 100h at a constant voltage of -0.534 V versus RHE (iR-uncorrected) with slight activity decay at high current densities.…”