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Boron-doped diamond (BDD) electrodes have a wide potential window and can produce ozone by water electrolysis at high voltage. Though ozone has strong oxidative power (standard oxidation potential: 2.07 V vs. NHE), it cannot decompose certain types of recalcitrant organic matter completely. We developed an advanced oxidation process (AOP), in which hydroxy radicals with stronger oxidative power (standard oxidation potential: 2.85 V vs. NHE) are formed using a combination of ozone, photocatalyst, and UV. In this study, we fabricated a mesoporous TiO2/BDD hybrid electrode and examined its potential for AOPs. A synergetic effect between electrochemical water treatment and photocatalytic water treatment was observed with the hybrid electrode that did not occur with the BDD electrode.

Ag-loaded boron-doped diamond (BDD) electrodes are used for photo-electrochemical reduction of CO2 to CO. The advantage of the electrode would be highlighted by the CO2 reduction at more positive potentials than that for electrochemical CO2 reduction on Ag electrodes. In the present study, we achieved a positive shift in the potential of Ag-loaded BDD electrodes prepared by two steps: namely, a pre-treatment of the BDD surface by cathodic electrolysis in an acidic solution and electrodeposition of Ag co-catalysts. The effects of the pre-treatment on the crystal structure and the chemical states on the surface of BDD were investigated by spectroscopic analysis with Raman scattering and X-ray photoelectron. The pre-treated Ag-loaded BDD electrode exhibited a positive shift in the apparent onset potential (− 0.18 V) in the current–voltage (I–V) curves of a CO2-purged 25 mM Na2SO4 solution under irradiation by ultraviolet light (222 nm). These results were compared with the potential of an electrode based on as-prepared BDD (− 0.64 V) under the same conditions. We applied a potential of − 0.61 V and analyzed the formation of CO by gas chromatography to confirm a nFE greater than 70% for the pre-treated Ag-loaded BDD electrode. The I–V curves and CO production were also investigated in the absence of ultraviolet light and the Ag co-catalysts. We discuss the factors that contributed to the positive shift in the potential for photo-electrochemical CO2 reduction on Ag-loaded BDD electrodes.

There is a need for highly efficient photocatalysts, particularly for water purification. In this study, we fabricated a mesoporous TiO2 thin film on a boron-doped diamond (BDD) layer by a surfactant-assisted sol-gel method, in which self-assembled amphiphilic surfactant micelles were used as an organic template. Scanning electron microscopy revealed uniform mesopores, approximately 20 nm in diameter, that were hexagonally packed in the TiO2 thin film. Wide-angle X-ray diffraction and Raman spectroscopy clarified that the framework crystallized in the anatase phase. Current&ndash, voltage (I&ndash, V) measurements showed rectification features at the TiO2/BDD heterojunction, confirming that a p&ndash, n hetero-interface formed. The as-synthesized mesoporous TiO2/BDD worked well as a photocatalyst, even with a small volume of TiO2 (15 mm &times, 15 mm &times, c.a. 1.5 &micro, m in thickness). The use of deep UV light (&lambda, = 222 nm) as a light source was necessary to enhance photocatalytic activity, due to photo-excitation occurring in both BDD and TiO2.

Competitive hydrogen evolution and multiple proton-coupled electron transfer reactions limit photoelectrochemical CO2 reduction in aqueous electrolyte. Here, oxygen-terminated lightly boron-doped diamond (BDDL) thin films were synthesized as a semiconductor electron source to accelerate CO2 reduction. However, BDDL alone could not stabilize the intermediates of CO2 reduction, yielding a negligible amount of reduction products. Silver nanoparticles were then deposited on BDDL because of their selective electrochemical CO2 reduction ability. Excellent selectivity (estimated CO:H2 mass ratio of 318:1) and recyclability (stable for five cycles of 3 h each) for photoelectrochemical CO2 reduction were obtained for the optimum silver nanoparticle-modified BDDL electrode at −1.1 V vs. RHE under 222-nm irradiation. The high efficiency and stability of this catalyst are ascribed to the in situ photoactivation of the BDDL surface during the photoelectrochemical reaction. The present work reveals the potential of BDDL as a high-energy electron source for use with co-catalysts in photochemical conversion.

Competitive hydrogen evolution and multiple proton-coupled electron transfer reactions limit photoelectrochemical CO2 reduction in aqueous electrolyte. Here, oxygen-terminated lightly boron-doped diamond (BDDL) thin films were synthesized as a semiconductor electron source to accelerate CO2 reduction. However, BDDL alone could not stabilize the intermediates of CO2 reduction, yielding a negligible amount of reduction products. Silver nanoparticles were then deposited on BDDL because of their selective electrochemical CO2 reduction ability. Excellent selectivity (estimated CO:H2 mass ratio of 318:1) and recyclability (stable for five cycles of 3 h each) for photoelectrochemical CO2 reduction were obtained for the optimum silver nanoparticle-modified BDDL electrode at −1.1 V vs. RHE under 222-nm irradiation. The high efficiency and stability of this catalyst are ascribed to the in situ photoactivation of the BDDL surface during the photoelectrochemical reaction. The present work reveals the potential of BDDL as a high-energy electron source for use with co-catalysts in photochemical conversion.