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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]

The high-speed three-dimensional movement dynamic friction polishing (3DM-DFP) has been recognized as an efficient approach for ultra-smoothing single crystal diamond (SCD) surface. Continuing from the previous works focusing on the subsurface cleavage of diamond after 3DM-DFP, process optimization and surface reaction evolution mechanism as a fundamental building block is investigated, for the first time, for comprehensively understanding this fast-smoothing manner. By systematically adjusting the controlling factor, stronger load (0.3 MPa) and appropriate duration (0.5 h) as well as moderate sliding speed (in the range of 30 to 45 m s−1) is found to be able to obtain the smooth surface of SCD without uncontacted traces or break-surface cleavage. Subtle residual clues on SCD surface as a function of progressive DFP procedure indicate that Fe catalytic oxidation mainly produce Fe 2 O 3 and partial intermediate oxides Fe 1-y O. Meanwhile, the activated oxygen inserts sp 3 C C bonds could form C O or C O and C-O-V (vacancy) at existing reactive surface sites. The (100) favorable C O bonds can be rebuilt if (100) surface is reformed, although the C O bonds associated with non-(100) rough surface would replace them during DFP procedure. The formed C O C and concomitant C-O-V as well as the oxidized graphite give rise to the increase of C O proportion, and finally the covered defective graphitic phase has an approximate C O/C O ratio of 1.25. All these are endowed potential value for future upgrading of DFP technique for diamond surface smoothing. [Display omitted] • The understanding of high-speed 3DM-DFP is further built by optimally control together with previous works. • The smooth surface with roughness <1 nm was obtained without uncontacted traces and extended cleavage. • Comprehensive polishing mechanism of SCD by high-speed 3DM-DFP was discussed. • Surface carbon‑oxygen bonds evolution is carefully studied based on the polishing procedure. [ABSTRACT FROM AUTHOR]