Abstract The influence of the porous structure of electrolytic nickel deposits (foams) and a Co–Mo–P–O catalyst on the hydrogen evolution reaction in an alkali solution is studied. Porous nickel deposits with an average thickness of 55 and 135 μm are prepared by the electrolysis of a solution containing 0.2 mol/L NiCl2 and 2 mol/L NH4Cl (pH 3.2) at a current density of 0.3 A/cm2 based on the geometric surface area of the electrode. A layer of the Co–Mo–P–O catalyst is deposited on the foam surface from a solution containing 0.15 mol/L CoSO4, 0.05 mol/L Na2MoO4, 0.15 mol/L Na3Cit, and 0.5 mol/L NaH2PO2 (pH 4) at a constant potential of –1.96 V relative to the saturated silver chloride electrode for 5 min. As found by energy dispersive X-ray spectroscopy, all elements of the catalyst are uniformly distributed over the sample surface. To estimate the electrochemically active surface area of the foams with the catalyst and without it, the impedance spectra are recorded in a 1 mol/L NaOH solution at a currentless potential when the electrode under study is close to an ideally polarizable electrode. The frequency ranges from 10 000 to 0.01 Hz, and the output signal amplitude is 10 mV. The electrochemically active surface area of the porous deposits under the conditions where no hydrogen bubbles are evolved is found to increase with increasing foam thickness but decreases after catalyst application. The application of the Co–Mo–P–O catalyst on the nickel foams decreases the charge-transfer resistance by 2–3 times. The electrocatalytic properties of the porous materials toward the hydrogen evolution reaction in a 1 mol/L NaOH solution in the current density range from 0.05 to 0.3 A/cm2 are evaluated by the results of polarization studies. The Ki coefficient characterizing the depolarization fraction relative to the hydrogen evolution overvoltage on the smooth nickel electrode is used as a quantitative criterion of electrocatalytic properties under the vigorous gas evolution conditions. An increase in the porous layer thickness from 55 to 135 μm and Co–Mo–P–O catalyst application are found to increase the Ki coefficient. In a range of hydrogen evolution current densities of 0.1–0.2 A/cm2, the electrocatalytic effect on the nickel foam 135 μm thick with the catalyst is equal to the sum of effects from increasing porous electrode surface and influence of the Co–Mo–P–O catalyst on the smooth nickel electrode. The maximum electrocatalytic activity parameter (Ki = 61%) toward the hydrogen evolution reaction in a 1 mol/L NaOH solution is achieved on the nickel foams 135 μm thick with the Co–Mo–P–O catalyst at a cathode current density of 0.3 A/cm2.

Effect of a Co–Mo–P–O Catalyst on the Electrochemical Properties of Electrolytic Nickel Foams

期刊论文
发表日期：

2025年2月1日

查看全文

V. S. Nikitin,
Yu. A. Moiseev,
T. N. Ostanina,
A. B. Darintseva

摘要

Abstract

The influence of the porous structure of electrolytic nickel deposits (foams) and a Co–Mo–P–O catalyst on the hydrogen evolution reaction in an alkali solution is studied. Porous nickel deposits with an average thickness of 55 and 135 μm are prepared by the electrolysis of a solution containing 0.2 mol/L NiCl₂ and 2 mol/L NH₄Cl (pH 3.2) at a current density of 0.3 A/cm² based on the geometric surface area of the electrode. A layer of the Co–Mo–P–O catalyst is deposited on the foam surface from a solution containing 0.15 mol/L CoSO₄, 0.05 mol/L Na₂MoO₄, 0.15 mol/L Na₃Cit, and 0.5 mol/L NaH₂PO₂ (pH 4) at a constant potential of –1.96 V relative to the saturated silver chloride electrode for 5 min. As found by energy dispersive X-ray spectroscopy, all elements of the catalyst are uniformly distributed over the sample surface. To estimate the electrochemically active surface area of the foams with the catalyst and without it, the impedance spectra are recorded in a 1 mol/L NaOH solution at a currentless potential when the electrode under study is close to an ideally polarizable electrode. The frequency ranges from 10 000 to 0.01 Hz, and the output signal amplitude is 10 mV. The electrochemically active surface area of the porous deposits under the conditions where no hydrogen bubbles are evolved is found to increase with increasing foam thickness but decreases after catalyst application. The application of the Co–Mo–P–O catalyst on the nickel foams decreases the charge-transfer resistance by 2–3 times. The electrocatalytic properties of the porous materials toward the hydrogen evolution reaction in a 1 mol/L NaOH solution in the current density range from 0.05 to 0.3 A/cm² are evaluated by the results of polarization studies. The K_i coefficient characterizing the depolarization fraction relative to the hydrogen evolution overvoltage on the smooth nickel electrode is used as a quantitative criterion of electrocatalytic properties under the vigorous gas evolution conditions. An increase in the porous layer thickness from 55 to 135 μm and Co–Mo–P–O catalyst application are found to increase the K_i coefficient. In a range of hydrogen evolution current densities of 0.1–0.2 A/cm², the electrocatalytic effect on the nickel foam 135 μm thick with the catalyst is equal to the sum of effects from increasing porous electrode surface and influence of the Co–Mo–P–O catalyst on the smooth nickel electrode. The maximum electrocatalytic activity parameter (K_i = 61%) toward the hydrogen evolution reaction in a 1 mol/L NaOH solution is achieved on the nickel foams 135 μm thick with the Co–Mo–P–O catalyst at a cathode current density of 0.3 A/cm².