Mitigating the massive emissions of greenhouse gases is one of the main measures taken to resolve the current growing climate problems. The electrochemical reduction of carbon dioxide to economically valuable chemical fuels has attracted the intensive attention of scholars. This review provides an overview of the application of conductive diamond in electrocatalytic reduction and outlines the improvement of electrochemical properties by employing metal particles to modify the surface. Meanwhile, the carbon-based electrode materials represented by glassy carbon and diamond-like carbon also have broad research value. Emphasis is placed on the electrochemical properties of boron-doped, transition metal modification and co-doped diamond film electrodes with appropriate extensions respectively. The carbon-chain compounds produced by the reduction reaction are also briefly described, which mainly focus on formic acid and ethanol. In addition, the development directions of electrochemical reduction technology are prospected.

Substrate has an essential influence on the growth process of diamond grains and the quality of the diamond coating. In this paper, the diamond coatings on Co-cemented tungsten carbide (WC-Co) and silicon nitride (Si3N4) substrates were deposited by hot filament chemical vapor deposition (HFCVD) technique to study the effect of growth process on adhesive strength of coating. The WC-Co and Si3N4 substrates were treated by etching and polishing process, respectively. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy were used to characterize the diamond coatings. Furthermore, the adhesive strength and tribological properties of the as-deposited diamond coatings were evaluated by indentation tests and dry sliding tests. The results showed that the diamond coating deposited on WC-Co had a considerable stronger adhesive strength and a higher friction coefficient than that on Si3N4, which may partly result from the flat surface morphologies of Si3N4 substrate that was due to no etching pretreatment. Thereafter, a novel etching method for Si3N4 surfaces by hydrofluoric acid (HF) was proposed to roughen the surface, and a new diamond coating with enhanced adhesive strength was fabricated on Si3N4. Hence, for the hard substrate, etching the surface, rather than polishing the surface, played an importance role on improving the adhesion strength of diamond coating.