Active and Robust Doped Transition Metal Systems (DTMS) As Electro-Catalysts for Hydrogen Evolution Reaction in Electrolytic and Photoelectrochemical Water Splitting

Abstract

Increased environmental pollution due to vast fossil-fuel consumption has necessitated efficient use of energy while exploring clean and non-carbonaceous fuel to address the increasing global energy demand.1 Hydrogen, as the most lightweight fuel, has the ability to provide a clean, reliable and affordable energy supply without any greenhouse gas emission.1 However, efficient and economic production of hydrogen, along with cost effective storage and distribution are the major bottlenecks for the commercial deployment of hydrogen as a fuel. There is therefore a critical need to address these issues.2-6 Electrolytic water splitting is considered as a promising approach for the economic and efficient production of hydrogen, as it does not involve greenhouse gas emissions and toxic byproducts.7 However, the high capital cost, mainly due to use of expensive noble metal electro-catalysts (e.g. Pt, IrO2, RuO2) is a major impetus for the development of non-PGM catalyst based PEM water electrolysis system. Engineering of non-noble metal electro-catalysts with high electrochemical activity for hydrogen evolution reaction (HER) will offer some reduction in the overall capital cost of PEM based water electrolysis systems. It is hence, important to identify electro-catalysts for HER (for use as the cathode of PEM water electrolyzers) with similar/lower overpotential, similar/superior cathodic current density (i.e., electrochemical activity) and similar/superior long term stability as that of state of the art Pt/C.In the present study, nanostructured DTMS based electro-catalysts have been studied for HER using first principles calculations. The results of the theoretical studies are experimentally verified by synthesizing the DTMS electro-catalyst nanoparticles. The TEM image of synthesized nanoparticles (NPs) is shown in Fig. 1. The electrochemical characterization of DTMS as cathode electro-catalysts for PEM water electrolysis system has been carried out using 0.5 M sulfuric acid (H2SO4) electrolyte (pH~0), 1 M potassium phosphate buffer (pH 7), 1 M KOH (pH 14), Pt wire counter electrode and Hg/Hg2SO4 reference electrode (+0.65V vs NHE) at a scan rate of 10 mV/sec and temperature of 26oC. The DTMS catalysts exhibit onset overpotential for HER similar to Pt/C (~10 mV vs RHE). The overpotential required to obtain current density of ~100 mA/cm2is similar to that of Pt/C in acidic, neutral and basic media, indicating the excellent electrochemical activity for HER. Moreover, the DTMS catalyst exhibits electrochemical stability in acidic media similar to that of Pt/C reflecting its potential as an alternative low cost non-PGM electro-catalyst system. Additionally, these novel electro-catalysts with unique composition and electronic structure also show promising response as the cathode electro-catalysts in PEC water splitting cell. The results of the synthesis, microstructural characterization, theoretical first principles study and electrochemical activity of these novel electro-catalysts will thus be presented and discussed.