Synthesis and Modification of the Surface of Electrolytic Nickel Foams as Catalytically Active Electrode Materials for Hydrogen Production by Electrolysis

Abstract—Porous nickel deposits (foams) are synthesized from a solution containing 0.2 mol/L NiCl2 and 2 mol/L NH4Cl (pH 3.2) under galvanostatic electrolysis conditions at a current density of 0.3–0.9 A/cm2 and an electrolysis time of 5–15 min. Using electrochemical deposition, a layer of the Co–Mo–P–O catalyst is applied for 5 min on the foam surface from a solution of 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 a saturated silver chloride electrode. Using scanning electron microscopy (SEM), the Co–Mo–P–O catalyst is found to be deposited not only on the outer surface of the foam but also on the inner surface of large pores. The linear voltammetry results show that the modification of the surface of the electrolytic nickel foams by Co–Mo–P–O catalyst application decreases an overvoltage of hydrogen evolution in an aqueous solution of 1 mol/L NaOH compared to the foams without a catalyst. As a criterion for the catalytic properties of the nickel foams, the coefficient Ki = 0.3 is calculated characterizing the depolarization fraction relative to the hydrogen evolution overvoltage on smooth nickel at a current density of 0.3 A/cm2. The regression equations are derived by the full factorial experiment method, which makes it possible to predict conditions for the synthesis of nickel foams and modification of their surface by applying the Co–Mo–P–O catalyst to form materials with high catalytic properties toward hydrogen evolution during the electrolysis of an alkali solution (1 mol/L NaOH). An analysis of the response surfaces shows that the use of the Co–Mo–P–O catalyst not only increases the catalytic properties of the nickel foams toward the hydrogen evolution reaction (HER) in an alkali solution but also allows the achievement of the highest value of Ki = 0.3 ≈ 60% on the foams of a lower thickness (prepared at a lower current density of 0.3 A/cm2) during 15-min electrodeposition. This material can be recommended for use as electrodes for producing hydrogen by the electrolysis of an alkali solution.