Performant Non-Precious Metal-Oxide Electrocatalysts for Oxygen Evolution Reaction in Alkaline Media: From Electrochemical Treatments of Ni Substrates to Surfactant-Assisted Electrodeposition of Perovskites

Abstract

To meet the global energy demand in a sustainable way, the development of reliable and efficient energy storage systems seems crucial. One of the attractive ways to store energy is through water electrolysis, producing hydrogen as an energy carrier (1). This process is limited by the sluggish kinetics of the oxygen evolution reaction (OER) occurring at the anode of an electrolyzer (eq. 1) (1). 4OH- → O2 + 2H2O + 4e- (Eo 298 = 0.401 VSHE) (1) In the alkaline media, a wide range of electrocatalyst materials including both precious and non-precious group metal compounds such as IrO2, RuO2, nickel oxides, manganese oxides, FeNiOx and perovskites have been intensively studied for OER electrocatalysis (2-8). Among these oxides, manganese oxides along with cobalt-based perovskites (e.g. LaCoOx) have shown promising electrocatalytic activity and long-term durability toward OER (2, 5, 7, 8). To alleviate the low electrical conductivity of such oxides, carbon-based materials are widely being used as catalyst supports and backing layers (5, 9, 10). However, typical carbonaceous materials suffer durability issues mainly caused by carbon corrosion at the high anodic potentials corresponding to the OER (11, 12). The Nickle-based electrodes have been employed in such applications in alkaline media to avoid the carbon corrosion showing high electrocatalytic activity and durability toward OER (13, 14). This study aims at investigating electrocatalytic activity and long-term stability of manganese oxides and perovskites deposited on Ni foams. Novel chemical and electrochemical treatments on the Ni foam substrates have been employed to enhance the durability of the deposited oxides. The deposited manganese oxide has provided the lowest initial OER overpotentials of between 210-230 mV at 10 mA cm-2, losing about 20 mV over 1 hr of testing (Fig. 1). The surfactant-assisted LaCoOx deposit has shown excellent durability over 1 hr of testing with an OER overpotential of about 260 mV at 10 mA cm-2. The electrochemical treatments of the Ni foam substrates have significantly decreased the OER overpotentials of the deposited oxides while increasing their long-term durability for OER through enhanced adhesion of the electrocatalysts to the treated Ni substrates. Figure 1. OER benchmarking study of the electrodeposited non-PGM electrocatalysts. The conditions are as follows: MnOx (T): MnOx electrodeposited in presence of Triton X-100. LaCoOx (T): LaCoOx electrodeposited in presence of Triton X-100. Acid-etched Ni: Mixed acid treatment on the Ni foam. CV Ni: Cyclic voltammetry treatment on the Ni foam for 10 cycles in 45 wt% KOH at 293 K. LSV5: Linear sweep voltammetry treatment on the Ni foam for 5 sweeps in 45 wt% KOH at 293 K. CA1: Chronoamperometry treatment on the Ni foam for 1 min in 45 wt% KOH at 293 K. Test conditions are: 10 mA cm-2. 45 wt% KOH. 400 rpm. 323 K.