Manganese-Based Electrocatalysts for Acidic Oxygen Evolution: Development and Performance Evaluation

Currently, the growing demand for sustainable hydrogen makes the oxygen evolution reaction (OER) increasingly important. To boost the performance of electrochemical cells for water electrolysis, both cathodic and anodic sides need to be optimized. Noble metal catalysts for the OER suffer from high costs and limited availability; therefore, developing efficient, low-cost alternatives is crucial. This work investigates manganese-based materials as potential noble-metal-free catalysts. Mn antimonates, Mn chlorates, and Mn bromates were synthesized using ultrasound-assisted techniques to enhance phase composition and homogeneity. Physicochemical characterizations were performed using X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM), together with energy-dispersive X-ray spectroscopy (EDX) and surface area analyses. All samples exhibited a low surface area and inter-particle porosity within mixed crystalline phases. Among the catalysts, Mn_7.5O₁₀Br₃, synthesized via ultrasound homogenization (30 min at 59 kHz) and calcined at 250 °C, showed the highest OER activity. Drop-casted on Fluorine-Doped Tin Oxide (FTO)-coated Ti mesh, it achieved an overpotential of 153 mV at 10 mA cm^-2, with Tafel slopes of 103 mV dec^-1 and 160 mV dec^-1 at 1, 2, and 4 mA cm^-2 and 6, 8, 10, and 11 mA cm^-2, respectively. It also demonstrated good short-term stability (1 h) in acidic media, with a strong signal-to-noise ratio. Its short-term stability is comparable to that of the benchmark IrO₂, with a potential drift of 15 mV h^-1 and a standard deviation of 3 mV for the best-performing electrode. The presence of multiple phases suggests room for further optimization. Overall, this study provides a practical route for designing noble metal-free Mn-based OER catalysts.