Nanostructured manganese oxide on frozen smoke: A new water-oxidizing composite

The water-oxidizing complex or oxygen-evolving complex in plants, algae and cyanobacteria is an Mn₄CaO₅ cluster catalysing light-induced water oxidation. Herein we report that nano-sized Mn oxide/carbon aerogel is an active and low-density catalyst toward water oxidation. The composite was synthesized by a simple, low-cost procedure with different ratio of carbon aerogel to Mn oxide and characterized by scanning electron microscopy, energy-dispersive spectroscopy, high resolution transmission electron microscopy, X-ray diffraction, electronic spectroscopy, Fourier transform infrared spectroscopy, and atomic absorption spectroscopy. Then, the water-oxidizing activity of this composite was considered in the presence of cerium(IV) ammonium nitrate. The composites with a high ratio of Mn oxide to carbon aerogel are good Mn-based catalysts with turnover frequencies of ∼0.33 (mmol O₂/(mol Mn·s)). In addition to the water-oxidizing activities of these composites under different conditions, their self-healing reaction in the presence of cerium(IV) ammonium nitrate was studied. We also compare the composite with graphene quantum dots/Mn oxide, which is not stable under these conditions. Using hydrogen to store sustainable energies is a promising strategy in the near future and our results show that nano-sized Mn oxide/carbon aerogel is a promising catalyst for water-splitting systems toward hydrogen evolution.