Advanced nitrogen-doped transition metal oxides decorated with Pt: synthesis and composition strategies for maximised electrochemical performance

Abstract

Developing efficient, low-cost catalysts for oxygen reduction and evolution reactions (ORR and OER) is key to advancing metal-air batteries and regenerative fuel cells. In this study, nitrogen-doped binary metal (Mn and Ni) oxides (N-BMOs) and Pt-decorated N-BMOs were synthesised using three methods and tested as ORR and OER catalysts in alkaline media. Their physicochemical properties were characterised by XRD, N2-sorption, TEM, and XPS, while their electrochemical performance was evaluated using voltammetry and impedance spectroscopy. Among all tested materials, the best bifunctional catalyst proved to be Pt/N-Mn2O3-NiO (1 : 1) (S3) with the highest achieved diffusion limited current density (-4.98 mA cm-2 at 1800 rpm), the highest kinetic current density (-15.3 mA cm-2), low Tafel slope (75 mV dec-1) in ORR potential region, and overpotential of 0.56 V to reach benchmark current value of 10 mA cm-2 during OER. The ΔE was calculated to be 0.95 V, comparable to or even better than that of similar materials reported in the literature. Pt/N-Mn2O3-NiO (1 : 1) (S3) demonstrated striking stability during long-term operation with preserved morphology and catalytic activity.