Pt/C/Ni(OH)₂Bi-Functional Electrocatalyst for Enhanced Hydrogen Evolution Reaction Activity under Alkaline Conditions

Abstract

The kinetics of hydrogen evolution and hydrogen oxidation reactions (HER/HOR) in alkaline electrolyte on Pt/C and a Pt/C/Ni(OH) 2 bi-functional electrocatalyst were studied. The objective was to investigate the enhancement of hydrogen evolution activity of Pt in alkaline environments in presence of transition metal hydroxides, and to determine the optimum concentration of Ni(OH) 2 to be added to maximize catalytic activity. The catalysts were prepared by mixing colloidal dispersions of nanosized Ni(OH) 2 with a commercially-sourced Pt/C catalyst dispersed in water. Rotating disk electrode (RDE) measurements were performed in 0.1 M KOH at temperatures ranging from 273.15 K to 303.15 K, and the HOR/HER kinetic currents, obtained after IR and mass transport corrections, were fitted using the Butler-Volmer equation to estimate the exchange current densities at each temperature. Arrhenius plots showed very similar activation energies for Pt/C (35 ± 6 kJ/mol) and the bi-functional catalysts (38 ± 6 kJ/mol) -Pt/C/X%Ni(OH) 2 . The maximum exchange current density (2.44 ± 0.07 mA cm −2 Pt at 303.15 K) was obtained with the catalyst containing 10 wt% Ni(OH) 2 , and was 2.4 times higher than for Pt/C (1.03 ± 0.07 mA cm −2 Pt at 303.15 K). The bi-functional catalysts were evaluated in a hydroxide-exchange membrane water electrolyzer operated with ultrapure water, and outperformed Pt/C by about 0.15 V across the entire current density range.

Tungsten Carbide Hollow Microspheres with Robust and Stable Electrocatalytic Activity toward Hydrogen Evolution Reaction

“…As well known, mass-transfer resistance could affect the HER performance at high current density because of the limited interfaces between electrocatalyst and electrolyte as well as coverage of active sites byproducts. As shown in Figure 3e,f, the HER performance of commercial Pt/C became better, especially for overpotential@100 mA cm –2 decreased from 128 to 105 mV with the rotation speed increased to 900 rpm because the strongly adhered H 2 bubbles were removed releasing more active sites similar to previous reports; 54,55 in contrast, W 2 C-HS revealed a stable HER activity with almost negligible decrement (2 mV) for overpotential@100 mA cm –2 because of the hollow structure of W 2 C-HS beneficial for the release of hydrogen molecular resulting in no deterioration in ECSA and interfacial charge resistance. Thus, the hollow structure was beneficial for HER electrocatalytic activity at high current density.…”

Processable Surface Modification of Nickel‐Heteroatom (N, S) Bridge Sites for Promoted Alkaline Hydrogen Evolution

“…Generally,HER involves the first two intermediate steps (Volmer and Heyrovsky step) in alkaline media. [13] To facilitate both steps,anideal catalyst for HER should satisfy the following requirements:( i) Fast water dissociation and appropriate adsorption energy to hydrogen at Volmer step; (ii)Low adsorption energy to hydrogen at the Heyrovsky step, thus H ads can chemically bond to another Htoform molecular hydrogen and detach from the catalyst surface.I ti sk nown that an N-functionalized surface can improve the hydrophilicity of am aterial surface.T hus,t he surface wettability behavior of the prepared samples before and after N-treat-ment was assessed by evaluating their contact angle differences.A ss hown in Figure S19, compared with the bare Ni sample,t he Ni À N 0.19 electrode exhibited an improved wettability,a se videnced by the significantly reduced contact angle.For the NiÀN 0.19 electrode,the hydrophilic domains can facilitate the dissociation of water and the production of hydrogen intermediates.T he produced Hi ntermediate can then adsorb onto the metallic Ni surface and recombine into molecular hydrogen, [14] while the N-covered hydrophilic surface can promote both the onset of the OH À adsorption and desorption, as the vital role played by the metal oxide/ hydroxide at the Pt surface during HER. [1b, 15] To gain further insights into the HER catalytic mechanisms of Ni(111) with adsorbed Na toms,w ep erformed as eries of density functional theory (DFT) calculations to investigate the catalytic reactions for Ni(111) with surface anchored Natoms (see details in the supporting information) by calculating the Gibbs free energy of H* adsorption (DG H* ), which has proven to be ak ey descriptor to characterize the HER activity of the electrocatalysts.…”

“…For the Ni−N 0.19 electrode, the hydrophilic domains can facilitate the dissociation of water and the production of hydrogen intermediates. The produced H intermediate can then adsorb onto the metallic Ni surface and recombine into molecular hydrogen, while the N‐covered hydrophilic surface can promote both the onset of the OH − adsorption and desorption, as the vital role played by the metal oxide/hydroxide at the Pt surface during HER …”

Palladium/Stannic Oxide Interfacial Chemistry Promotes Hydrogen Oxidation Reactions in Alkaline Medium

“…Each uniform electrocatalyst ink was then dropcasted onto previously polished GCE's surface and then dried in the air with calculated Pd loading (0.0199 mg pd cm À 2 ) for each electrocatalyst, following previously method. [71] The HOR experiments were performed in an instantly produced 0.1 M KOH solution and subsequently saturated with ultrapure hydrogen gas (H 2 ) at both controlled and varied temperatures in a thermostated water-bath. Potentials utilized in this work are converted to reversible hydrogen electrode (RHE = E Ag j AgCl + E o Ag j AgCl (0.197) + 0.059 pH, where pH = 12.57).…”