Improved bi-functional oxygen electrocatalytic performance of Pt–Ir alloy nanoparticles embedded on MWCNT with Pt-enriched surfaces

Abstract

Multi-walled carbon nanotube supported Pt–Ir nanoparticles (Pt–Ir/MWCNT) with different elemental ratios were synthesized by one-pot co-reduction approach under ambient conditions. The Pt–Ir catalysts exhibit improved bi-functional activity towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) and its electrocatalytic performance was clearly established using different physiochemical characterization techniques. The Pt–Ir composition of 2:1 has a higher electrochemical surface area (ECSA) of about 85.3 m2/g compared to other compositions (3:1 and 1:1) and Pt/MWCNT due to the effect of particle size distribution. The improved ORR/OER activity was found to be 139.4 and 740 mA/mg, respectively, for Pt–Ir(2:1)/MWCNT with the potential difference of 760 mV for oxygen bi-functional activity. Furthermore, Pt–Ir(2:1)/MWCNT showed much better stability for ORR compared to other compositions and Pt/MWNCT catalysts, i.e., around 76% of its initial ECSA retained with <20 mV shift in half-wave potential was obtained even after 10,000 potential cycles in acidic medium. It is believed that the Pt enriched surface, amount of Ir content, induced electronic and geometric effects play a vital role on the electrocatalytic activity enhancement of Pt–Ir(2:1)/MWNCT as effective bi-functional oxygen electrode.