Tailoring manganese oxide nanoplates enhances oxygen evolution catalysis in acid

• Single-phase Mn 3 O 4 nanoplates OER electrocatalyst was fabricated. • A simple method to analyze effect of heating on phase transition was proposed. • R20-Mn sample is highly efficient and stable for OER in acidic media. • Enhancement of OER activity is attributed to single phase and 2D nanostructure. Achieving active and stable oxygen evolution reaction (OER) in acid media is highly promising towards cost-effective and sustainable proton exchange membrane (PEM) electrolyzers, especially driven by the two-dimensional (2D) nanostructured catalysts. Here, we report a single-phase manganese tetroxide nanoplates (R20-Mn) by simply rapid annealing of manganese chloride tetrahydrate in air as an efficient and durable electrocatalyst for acidic OER. Agreeing well with the theoretical calculations of significantly reduced overpotentials compared with commercial RuO 2 catalyst, R20-Mn delivers an exceptionally intrinsic activity, achieving ultralow overpotentials of 210 mV at a current density of 10 mA cm −2 for OER under acidic media. Therefore, this work provides an important complement to design 2D single-phase transition metal oxides catalysts with prominent activity in acidic water electrolysis.