Dual Improvement of β ‐MnO 2 Oxygen Evolution Electrocatalysts via Combined Substrate Control and Surface Engineering

The development of catalysts with high intrinsic activity towards the oxygen evolution reaction (OER) plays a critical role in sustainable energy conversion and storage. Herein, we report on the development of efficient (photo)electrocatalysts based on functionalized MnO 2 systems. Specifically, β ‐MnO 2 nanostructures grown by plasma enhanced‐chemical vapor deposition on fluorine‐doped tin oxide (FTO) or Ni foams were decorated with Co 3 O 4 or Fe 2 O 3 nanoparticles by radio frequency sputtering. Upon functionalization, FTO‐supported materials yielded a performance increase with respect to bare MnO 2 , with current densities at 1.65 V vs . the reversible hydrogen electrode (RHE) up to 3.0 and 3.5 mA/cm 2 in the dark and under simulated sunlight, respectively. On the other hand, the use of highly porous and conductive Ni foam substrates enabled to maximize cooperative interfacial effects between catalyst components. The best performing Fe 2 O 3 /MnO 2 system provided a current density of 17.9 mA/cm 2 at 1.65 V vs . RHE, an overpotential as low as 390 mV, and a Tafel slope of 69 mV/decade under dark conditions, comparing favorably with IrO 2 and RuO 2 benchmarks. Overall, the control of β ‐MnO 2 /substrate interactions and the simultaneous surface property engineering pave the way to an efficient energy generation from abundant natural resources.