Boron doped cryptomelane as a highly efficient electrocatalyst for the oxygen evolution reaction

In this study, cryptomelane-type (1D) MnO2 was doped with boron powder by ball-milling in an inert organic solvent under various experimental conditions. The structural, thermal, morphological, and surface features of samples prepared by the ball-milling method were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy, and surface measurements. The electrocatalytic oxygen evolution reaction (OER) performances of the samples were tested and compared with the bare cryptomelane to reveal the effect of boron doping into manganese oxide. It was found that boron particles transformed to trigonal BO3 units in the cryptomelane structure via mechanical activation, and accordingly, the oxidation state of manganese in this structure relatively changed. The 0.25% B-doped cryptomelane sample prepared at 12 h grinding time exhibited the overpotential of 425 mV at a current density of 1 mAcm−2 with a Tafel slope of ∼95 mV dec−1. It showed a remarkable catalytic performance among the other electrocatalysts under neutral pH compared to bare cryptomelane. When the elemental boron doping exceeded 1%, the electrochemical performance dramatically decreased depending on the blocking of the Mn3+ active sites.