The generation of efficient, cheap and easily available water splitting catalysts, in particular for the oxygen evolution reaction (OER), is vital to the development of sustainable energy sources. Primary batteries, especially alkaline and Zn−C batteries, mostly end‐up in landfill due to their short lifespan which aggravates health and poses environmental threats. To address these issues, this work establishes a sustainable route for the generation of Manganese oxide (Mn3O4) from spent Zn−C batteries as a catalyst for the OER under alkaline conditions. A thermal transformation study is conducted here at 900 °C and 800 °C under controlled atmosphere to generate Mn3O4 nanoparticles from waste Zn−C batteries which are investigated as a potential OER catalyst. Mn3O4 particle synthesis was confirmed by XRD, Raman, FTIR, TEM and EDS analysis. The electrochemical performance demonstrated a low overpotential of 360 mV to reach 10 mA cm−2 with a Tafel slope of 64 mV dec−1 indicating good activity under alkaline conditions. Thus, the generation of Mn3O4 from a spent Zn−C battery that can be employed as a catalyst for the OER is a promising path not only for the effective extraction of resources from battery waste, but also for the exploitation of using extracted materials in advanced technology applications.