Hierarchically porous calcium-containing manganese dioxide nanorod bundles with superior photoelectrochemical activity

Bioinspired by the composition of the oxygen evolving complex and the fundamental role of calcium for catalysis, we have synthesized calcium-manganese oxides as promising photoelectrodes. We report the first demonstration of hierarchically porous Ca-containing MnO₂ nanorod (NR) bundles as visible-light-sensitive photofunctional nanoelectrodes to fundamentally improve the performance of MnO₂ for photoelectrochemical hydrogen generation. A substantial amount of Ca (up to 7.8 atom %) can be in situ incorporated into the MnO₂ lattice by a simple electroplating technique because of the exceptionally small feature sizes of several nanorods. The maximum photocurrent could be successfully achieved as high as 0.42 mA cm^-2, which is the best value for a MnO₂ photoanode to date. Significantly, Ca-containing MnO₂ photoanodes illustrated striking photoelectrochemical activity in response to visible light with a high incident photon-to-current conversion efficiency of 7 % at a monochromatic wavelength of 450 nm. The improvement in photoactivity of photoelectrochemical response may be attributed to the enhanced visible-light absorption, increased charge-carrier densities, and large contact area with electrolyte owing to the synergistic effects of Ca incorporation and specific mesopore networks, thus contributing to photocatalysis. The new design of constructing highly photoactive Ca-containing MnO₂ nanorod bundles sheds light on developing high-efficiency photoelectrodes for solar hydrogen generation. Bundle of nanojoy: A high-activity model in photocatalytic nanosystem is designed comprising mesoporous Ca-containing MnO₂ nanorod bundles that are visible-light-sensitive photofunctional electrodes that fundamentally improve the performance of MnO₂-based photoanodes for photoelectrochemical hydrogen generation. ITO=indium tin oxide.