Boron-doped diamond (BDD) electrodes are next generation electrode materials and their electrochemical applications have been actively developed in recent years. They are expected to be useful ...electrode materials for improving the environment and for bio-medical applications. Here, examples of practical applications as electrochemical sensors, the development of in vivo real time measurements, and electrochemical organic synthesis using BDD electrodes are briefly introduced. In the second part, our recent work on the production of useful chemicals by means of the electrochemical reduction of CO2 using BDD electrodes is described. The work has attracted particular attention for its potential contribution to carbon neutrality and carbon recycling.
High faradaic efficiencies can be achieved in the production of formic acid (HCOOH) by metal electrodes, such as Sn or Pb, in the electrochemical reduction of carbon dioxide (CO2). However, the ...stability and environmental load in using them are problematic. The electrochemical reduction of CO2 to HCOOH was investigated in a flow cell using boron‐doped diamond (BDD) electrodes. BDD electrodes have superior electrochemical properties to metal electrodes, and, moreover, are highly durable. The faradaic efficiency for the production of HCOOH was as high as 94.7 %. Furthermore, the selectivity for the production of HCOOH was more than 99 %. The rate of the production was increased to 473 μmol m−2 s−1 at a current density of 15 mA cm−2 with a faradaic efficiency of 61 %. The faradaic efficiency and the production rate are almost the same as or larger than those achieved using Sn and Pb electrodes. Furthermore, the stability of the BDD electrodes was confirmed by 24 h operation.
Diamonds for formic acid: From the electrochemical reduction of CO2 on boron‐doped diamond (BDD) electrodes using a circulation flow cell, formic acid could be obtained with high faradaic efficiency (up to 95 %). The stability of the BDD electrodes was confirmed by operating the system for 24 h. BDD electrodes are thus a viable alternative to metal electrodes for formic acid production.
The catalytic, electrocatalytic, or photocatalytic conversion of CO2 into useful chemicals in high yield for industrial applications has so far proven difficult. Herein, we present our work on the ...electrochemical reduction of CO2 in seawater using a boron‐doped diamond (BDD) electrode under ambient conditions to produce formaldehyde. This method overcomes the usual limitation of the low yield of higher‐order products, and also reduces the generation of H2. In comparison with other electrode materials, BDD electrodes have a wide potential window and high electrochemical stability, and, moreover, exhibit very high Faradaic efficiency (74 %) for the production of formaldehyde, using either methanol, aqueous NaCl, or seawater as the electrolyte. The high Faradaic efficiency is attributed to the sp3‐bonded carbon of the BDD. Our results have wide ranging implications for the efficient and cost‐effective conversion of CO2.
Boron is a diamond's best friend: A boron‐doped diamond (BDD) electrode exhibited very high Faradaic efficiency (74 %) for the production of formaldehyde using either methanol, aqueous NaCl, or seawater as the electrolyte at room temperature and ambient pressure.
The electrochemical oxidation reaction of nitrogen dioxide (NO2) using boron doped diamond (BDD) electrodes is presented. Cyclic voltammetry of NO2 in a 0.1 M KClO4 solution exhibits oxidation peaks ...at +1.1 V and +1.5 V (vs. Ag/AgCl) which are attributable to oxidation of HONO and NO2−, respectively. Moreover, the pH and scan rate dependences were investigated to study the oxidation mechanism. A linear calibration curve was observed in the concentration range of ∼1 to 5 mM (R2=0.99) with a detection limit of 11.1 ppb (S/B=3) for HONO and 58.6 ppb (S/B=3) for NO2−. In addition, the analytical performance was compared with those using glassy carbon, platinum and stainless steel as the working electrode.
The main product obtained by electrochemical reduction of CO2 depends on the electrode material, and in many cases the Faradaic efficiency for this is determined by the electrolyte. Only a few ...investigations in which attempts to produce different products from the same electrode material have been done so far. In this work, we focus on boron-doped diamond (BDD) electrodes with which plentiful amounts of formic acid and small amounts of carbon monoxide have been produced. By optimizing certain parameters and conditions used in the electrochemical process with BDD electrodes, such as the electrolyte, the boron concentration of the BDD electrode, and the applied potential, we were able to control the selectivity and efficiency with which carbon monoxide is produced. On one hand, with a BDD electrode with 1% boron used for the cathode and KClO4 for the catholyte, the selectivity for producing carbon monoxide was high. On the other hand, with a BDD electrode with 0.1% boron used for the cathode and KCl for the catholyte, the production of formic acid was the most evident. In situ attenuated total reflectance-infrared (ATR-IR) measurements during electrolysis showed that CO2 •– intermediates were adsorbed on the BDD surface in the KClO4 aqueous solution. Here, switchable product selectivity was achieved when reducing CO2 using BDD electrodes.
This study is among the first to systematically study the electrochemical reduction of nitrate on boron-doped diamond (BDD) films with different surface terminations and boron-doping levels. The ...highest nitrate reduction efficiency was 48% and the highest selectivity in the production of nitrogen gas was 44.5%, which were achieved using a BDD electrode with a hydrogen-terminated surface and a B/C ratio of 1.0%. C–H bonds served as the anchor points for attracting NO3− anions close to the electrode surface, and thus accelerating the formation of NO3−(ads). Compared to oxygen termination, hydrogen-terminated BDD exhibited higher electrochemical reactivity for reducing nitrate, resulting from the formation of shallow acceptor states and small interfacial band bending. The hydrophobicity of the hydrogen-terminated BDD inhibited water electrolysis and the subsequent adsorption of atomic hydrogen, leading to increased selectivity in the production of nitrogen gas. A BDD electrode with a boron-doping level of 1.0% increased the density of acceptor states, thereby enhancing the conductivity and promoting the formation of C–H bonds after the cathodic reduction pretreatment leading to the direct reduction of nitrate.
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•The surface termination and boron-doping level play major roles in nitrate reduction.•Hydrogen termination benefits the formation of NO3−(ads).•Hydrogen-terminated surfaces have higher electrochemical reactivity with nitrate.•BDD with a B/C ratio of 1% promotes the formation of C–H bonds thus enhancing nitrate reduction.
An electrogenerated chemiluminescence (ECL) system by in situ coreactant production, where Ru(bpy)3 2+ emission is generated at a boron-doped diamond (BDD) electrode, is presented. The system takes ...advantage of the unique properties of BDD to promote oxidation of carbonate (CO3 2–) into peroxydicarbonate (C2O6 2–), which further reacts with water to form hydrogen peroxide (H2O2), which acts as a coreactant for Ru(bpy)3 2+ ECL. Investigation of the mechanism reveals that ECL emission is triggered by the reduction of H2O2 to hydroxyl radicals (OH•), which later react with the reduced Ru(bpy)3 + molecules to form excited states, followed by light emission. The ECL signal was found to increase with the concentration of CO3 2–; therefore, with the concentration of electrogenerated H2O2, although at the same time, higher concentrations of H2O2 can quench the ECL emission, resulting in a decrease in intensity. The carbonate concentration, pH, and oxidation parameters, such as potential and time, were optimized to find the best emission conditions.
The electrochemical nitrate reduction by using boron-doped diamond (BDD) and copper (Cu) electrodes was investigated at various potentials. Product selectivity of nitrate reduction was strongly ...dependent on the applied potential for both electrodes. The highest selectivity of nitrogen gas production was obtained at −2.0 V (vs. Ag/AgCl) by using a BDD electrode with a faradaic efficiency as high as 45.2%. Compared with Cu electrode, nitrate reduction on BDD electrode occurred at more positive potential, and the production of nitrogen gas was larger. The transformation of surface-adsorbed nitrate into molecular nitrogen would be accelerated on BDD electrode with hindering nitrite production. In addition, low concentration of surface-adsorbed hydrogen on the BDD would also retard the ammonia generation, leading to increase in the selectivity of nitrogen gas formation. Meanwhile, BDD electrode could hinder the hydrogen evolution reaction, which enhanced the efficiency for nitrate reduction and decreased energy consumption. BDD electrode has excellent stability to remain better performance for reducing nitrate during electrolysis without any variation of surface morphology or chemical components.
•Products distribution of nitrate reduction depended on the applied potential.•BDD could reduce nitrate at more positive potential than Cu.•The highest faradaic efficiency of 45.2% for nitrogen gas production with BDD.•BDD could enhance the selectivity of nitrogen gas formation.•BDD retarded HER, so promoting nitrate reduction and decreasing energy consumption.
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