Fabrication of durable mono-electrocatalyst layer of MnOx nanostructures on graphite via facile electrodeposition for efficient electrooxidation of ammonia wastewater

A novel Pb- and Sb-free mono-electrocatalyst layer of manganese oxide (MnOx) structure is fabricated for efficient ammonia wastewater treatment, effectively addressing both catalyst stability and electrochemical performance. Various MnOx/graphite nanostructures are synthesized via electrodeposition, with optimized parameters enhancing electrode capacitance and stability. τ-MnO₂ nanospheres on etched graphite, incorporating silicon, aluminum, and sulfur, form a binder-integrated structure, demonstrating superior electrochemical activity and durability for ammonia oxidation. Cyclic voltammetry analysis reveals a high electrochemical surface area of 21.3 cm² at 0.7 V, coupled with enhanced oxygen evolution reaction (OER) activity. Tafel slope analysis shows faster electron transfer with increasing ammonia concentration at pH 12, highlighting the catalyst's adaptability to varying conditions. The τ-MnO₂/graphite electrode achieves 10 mA cm⁻²at 0.2 V and 0.6 V in ammonia solutions (100 mg-N L⁻¹, pH 10, 10 mV s⁻¹). Electrochemical impedance spectroscopy indicates excellent conductivity with low charge transfer resistance (Rct = 5.65 Ω). Notably, the τ-MnO₂ nanospheres maintain 94.7 % ammonium removal efficiency after 5000 cycles and 90 % ammonia electrooxidation efficiency over 40 h, demonstrating long-term stability. Multi-step electrochemical analysis reveals over 99 % ammonia degradation and 85 % N₂ production with minimal byproducts. These findings underscore the potential of MnOx/graphite electrodes for large-scale ammonia wastewater treatment and energy conversion.