Synthesis of amorphous Geobacter-manganese oxide biohybrid as efficient water oxidation catalysts

The development of low cost and efficient oxygen evolution reaction (OER) catalyst has paramount importance to meet future sustainable energy demand. Nature’s photosynthetic machinery deploy manganese-based complex in photosystem II to oxidize water. Inspired by nature, herein, we synthesized a high performing manganese-based OER catalyst using an electrochemically active and iron-rich bacterium, Geobacter sulfurreducens. The synthesized biohybrid catalyst (amorphous Geobacter-Mn2O3) produced a current density of 10 mA cm-2 at an overpotential of 290 ± 9 mV versus reversible hydrogen electrode with a low Tafel slope of 59 mV dec-1. The catalyst exhibited remarkable stability, evidenced through a long-term chronopotentiometry experiment. Multiple lines of evidence showed that G. sulfurreducens contributed OER active elements (iron and phosphorous) to the biohybrid catalyst and the as-synthesized Geobacter-Mn2O3 is amorphous. The amorphous structure of the biohybrid catalyst provided a large electrochemically active surface area and excess catalytic sites for the OER catalysis. In addition, Mn3+ present in the biohybrid catalyst is believed to be the precursor for oxygen evolution. The OER activity of the biohybrid catalyst outperformed commercial-Mn2O3, commercial-IrO2 and most of the benchmark precious OER catalysts; supporting its suitability for large-scale applications. The proposed green approach to synthesize biohybrid catalyst paves a new avenue to develop robust and cost-effective electrocatalysts for energy-related applications.