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Oxygen evolution reaction (OER) is critical in water splitting for green hydrogen gas production due to its sluggish kinetics; however, commercial OER catalysts commonly suffer from high cost, low catalytic activity and poor stability. Herein, we developed a C+ ion implantation method to modify single crystal diamond, and the resultant surface amorphous layer not only raised the active site number but also increased the content of the C=O group, thus significantly improving the OER activity. The C+ ion implanted high-temperature and high-pressure (C+-HTHP) and chemical vapor deposition (C+-CVD) diamonds both exhibit low OER overpotential with η 10 of 317 mV and 325 mV respectively, superior to those of HTHP diamond (360 mV), CVD diamond (395 mV) and RuO 2 (364 mV). The potentiostatic testing shows that the C+ implanted diamonds almost didn't undergo the rise of OER overpotential upon catalysis for more than 12 h at a current density of 10 mA cm−2, suggesting a high catalytic stability, owing to the strong bonding between single crystal diamond and amorphous carbon layer. For the first time, we utilized carbon ion implantation to prepare diamond-based high-performance OER catalyst, which broadens the understanding of carbon-based materials in OER catalysis. [ABSTRACT FROM AUTHOR]

Surface etching of single-crystal diamond (SCD) in hydrogen plasma plays a decisive role for high-quality homoepitaxy and surface conduction of diamond. The complexity of surface/subsurface condition such as defects would give rise to the distinct morphology features and even further result in the unpredictable properties. Correspondingly, the evolutionary relationship between the morphology and electrical properties of mechanically polished SCDs which have typical cleavage damage in microns depth after hydrogen plasma treatment still needs to be further completed. In this work, the chemical vapor deposited (CVD) SCDs with uniform polishing-caused subsurface cleavage were immersed in microwave hydrogen plasma for variable duration. Time-dependent morphological evolution, multi-mode etched pits (EPs) (resulting from local defects/cracks and dislocations) and associated etching mechanism were comprehensively studied. At the early stage of plasma treatment before 60 min, owing to the obvious surface roughing generated by preferential etching (with the rate of >400 nm/h) of severe mechanically damaged regions, the hole mobility was significantly deteriorated, also accompanying with the apparent drop of sheet concentration. Concurrently, the deposited surface sp 2 amorphous carbon (a -C) nanodots on diamond surface and non- sp 3 hydrogen bonds reconstruction, which arising from defect-etching produced local abundant carbon-containing radicals or possible exfoliation generated by hydrogen penetration of massive defective regions, also would play an adverse role for the conduction associated with (100) C–H surface. However, the surface roughness was reduced from the maximum 13.2 nm–4.2 nm by prolonging etching, resulting from the smoothing effect of small-angle crystal misorientation on waved height difference related to the uniform (111) cleavage and the removal of dense irregular EPs associated with polishing-induced local defects as well as the vanishing of surface a -C nanodots. In this case, the improvement of surface electrical properties together with the negative correlation of the mobility and sheet concentration were appeared by the gradual formation of (100) diamond surface and the building of uniform (100) C–H bonds. • CVD SCDs with typical subsurface damages(defects) were treated in pure hydrogen plasma. • Morphology evolution associated with polishing defects was time-dependently presented. • Surface sp2 nanodots deposition from defect-etching and CH reconstruction would affect electrical properties. [ABSTRACT FROM AUTHOR]