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.

Fuel cells generate power by converting chemical energy to electricity via electrochemical reactions, which involve eco-friendly reactants and products, in comparison to conventional power generators based on the internal combustion engine. Accordingly, the fuel cell is an attractive and promising power generator with a wide range of applications in sensors, portable devices, automotives, and stationary power systems. The direct methanol fuel cell (DMFC) resembles the proton exchange membrane fuel cell (PEMFC) in its power-generating unit, and the membrane electrode assembly (MEA) with a proton exchange-membrane that is sandwiched between two electrodes. However, instead of hydrogen gas, which is used as fuel in a PEMFC, the DMFC uses a methanol solution as the fuel feeding the anode. The methanol is oxidized to CO 2 , via an electrochemical process, at the anode and the air is reduced at the cathode to generate the electricity. With methanol solution as fuel, the DMFC system can be operated without a humidification unit, which is essential for the pure hydrogen PEM systems. The fact that methanol solution can be easily stored and refilled and hence can provide a relatively high energy density of 6.08 Whg À1 (neat methanol) makes the DMFC a potential solution as a mobile energy source. Therefore, the DMFC system, rather than a secondary battery (such as Li-ion battery), is regarded as a next-generation power source in a portable system.Despite all the advantages of DMFC, the sluggish methanol oxidation rate and the methanol crossover detrimentally affect its performance. A key technology for the development of DMFC is the development of a highly efficient MEA, in which the methanol can be easily and rapidly oxidized by the catalysts before it arrives at the membrane. As evident from literature, the uniform deposition of carbon-supported nanoscale catalysts, Pt-Ru with an atomic ratio of 1 : 1, coated on the gas diffusion layer (i.e., carbon cloth and carbon paper) has been widely adopted to provide the catalyst layer of the anode in the DMFC [1][2][3]. Besides the catalysts, the carbon support also markedly interferes with the MEA performance due to its role in Electrocatalysis of Direct Methanol Fuel Cells. Edited j315 stabilizing the catalysts, providing diffusion channels and conduction of the output electrons. Traditionally, carbon blacks (CBs), possessing moderate conductivity and large surface area, are widely adopted as the carbon supports. For example, Vulcan XC-72 with an electrical conductivity of 0.25 S cm À1 and a BETsurface area of 237 m 2 g À1 , is extensively used as carbon supports [4]. Although the CBs is normally selected as the support for the fuel cell, a new carbon support with higher conductivity and larger surface area is desired. Recently, carbon nanotubes (CNTs) with a large surface area, high electrical conductivity, and unique shape [5,6] have emerged as potential carbon supports in fuel cell applications. Numerous works have attempted to disperse platinum (Pt/CNT) or platinum-ruthenium...

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