Complementary Functions of Vanadium in Boosting Electrocatalytic Activity of CuCoNiFeMn High‐Entropy Alloy for Water Splitting

Abstract

High entropy alloys (HEAs) composed of multi‐metal elements in a single crystal structure are attractive for electrocatalysis. However, identifying the complementary functions of each element in HEAs is a prerequisite. Thus, VxCuCoNiFeMn (x = 0, 0.5, and 1.0) HEAs are investigated to identify the active role of vanadium in improving the electrocatalytic activity for the hydrogen evolution reaction (HER). Structural studies show the successful incorporation of V in the HEA. V1.0CuCoNiFeMn (V1.0‐HEA) shows an overpotential of 250 mV versus the reversible hydrogen electrode (at −50 mA cm−2, 1 m KOH), which is ≈170 mV lower than that of control‐HEA (422 mV). Improves electrical conductivity and the electrochemical surface area of the V1.0‐HEA accelerated HER activity. Furthermore, density functional theory calculations reveal reduced water dissociation and hydrogen adsorption energies of V1.0‐HEA, resulting in the boosted HER kinetics. The effect of V incorporation on the barrier height and active sites at the surface of V1.0‐HEA is schematically explained. This study can be facilitated for the development of highly active HEAs for large‐scale electrochemical water splitting.

Electrochemical Hydrogen Evolution Reaction Evaluation of CoNi(Cr/V) Medium-Entropy Alloys in an Acidic Environment

“…The Cr 2p 3/2 spectra in Figure (c) for CoNiCr and CoNi­(Cr/V) show double overlapping peaks at 574.2 and 575.7 eV, which correspond to Cr (0) metallic and Cr 3+ charge states, respectively . Similarly, V 2p 3/2 spectra (Figure (d)) in CoNiV and CoNi­(Cr/V) also show two doublets at B.E values of 512.6 and 514.3 eV, which are assigned to V (0) and V 3+ oxidation states, respectively . The existence of Cr 3+ and V 3+ valence states on the surface of pristine alloy samples may be due to exposure of samples to air, since the Cr and V are strong passivating transition metals …”

“…43 Similarly, V 2p 3/2 spectra (Figure 4(d)) in CoNiV and CoNi(Cr/V) also show two doublets at B.E values of 512.6 and 514.3 eV, which are assigned to V (0) and V 3+ oxidation states, respectively. 44 The existence of Cr 3+ and V 3+ valence states on the surface of pristine alloy samples may be due to exposure of samples to air, since the Cr and V are strong passivating transition metals. Tafel plots were recorded using the steady-state method reported in the literature.…”

Functional high-entropy alloys: promising catalysts for high-performance water splitting

“…Sivanantham and colleagues produced V-doped V x CuCoNiFeMn ( x = 0, 0.5, and 1.0) HEA catalysts and identified the positive role of V in enhancing the HER activity. 115 Among all the catalysts, V 1.0 -HEA exhibited exceptional HER activity, with an η 50 of 250 mV, equivalent to that of Pt/C ( η 50 of 207 mV), representing an improvement of approximately 80 mV over that of the unmodified catalyst. Theoretical calculations suggest that the improvement in electrocatalytic performance is attributed to the adjustment of the d-band center after V doping, which induced a balance in the adsorption free energy of the intermediates.…”

A review of noble metal-free high entropy alloys for water splitting applications

“…The coupling of multi-elements with different electronic properties of HEA catalysts is expected to fine-tune their adsorption energy. For example, Sivanantham et al 137 synthesized a V x CuCoNiFeMn ( x = 0, 0.5 and 1.0) HEA via a high-energy ball-milling process. Fig.…”