Evaluation of different Ni–semiconductor composites as electrodes for enhanced hydrogen evolution reaction

Abstract

The use of earth-abundant materials for designing efficient and stable electrocatalysts is of paramount importance to facilitate large-scale production of hydrogen. In this work we developed a new series of electrodes based on Ni-semiconductor composites (Ni|SC) that are easy to synthesize (binder-free, economic and readily scalable method of synthesis), highly stable and active towards electrochemical hydrogen production under alkaline conditions. We showed the direct electrodeposition of composites (Ni|SC) from nickel-Watts plating baths modified by the addition of Nb2O5, Nb3(PO4)5, Bi2O3 and WO3 semiconductor particles. The electrodes were characterized by different techniques (electron and confocal microscopy, X-ray spectroscopy, X-ray diffraction, Raman spectroscopy, among others) before and after their electrochemical evaluation as catalysts for hydrogen evolution from water. In order to gain insights into their structure-activity relationship, the materials were also characterized by means of electrochemical analyses, i.e., cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. All catalysts have onset potential values around -1.1 V vs. SCE and similar Tafel slopes (ca. 120 mV dec-1) corresponding to the Volmer reaction as the rate determining step of the reaction. These catalysts show an increase of up to 115% (for Ni|WO3) of hydrogen production current compared to conventional Ni catalysts, in most cases preserving great chemical and structural stability after short ageing under alkaline conditions. The composite catalysts were synthesized on low-cost nickel-plated stainless-steel supports, which make them excellent alternatives for replacing massive nickel electrodes in conventional alkaline electrolyzers.