Ion-Independent CO2 Reduction with Boron-Doped Diamond Electrodes for Sustained Formic Acid Production and In Situ Concentration

Recent chemical advancements have brought a variety of products but also increased emissions of harmful substances, prompting the search for cleaner synthesis methods like organic electrolytic synthesis methods, using electrical energy for reactions. Meanwhile, with the urgent need to reduce CO2 emissions and achieve carbon neutrality, recycling and reducing technologies for CO2 have gained significant attention 1). This study focuses on electrolytic carboxylation, utilizing CO2 as a raw material, which presents a promising avenue for organic electrolytic synthesis, allowing the synthesis of high-value compounds from cost-effective materials using electrical energy as a reducing agent. Notably, it offers the advantage of producing less waste, positioning it as a robust option for industrial adoption centered on green chemistry. However, since electrocarboxylation reactions occur on electrode surfaces, conventional approaches utilize organic solvents and precious metals like platinum (Pt), prized for their corrosion resistance and durability. To address this challenge, we have directed our focus towards synthesizing boron-doped diamond (BDD) electrodes, incorporating boron into the diamond structure. BDD electrodes boast a wide potential window, high durability, and corrosion resistance, making them capable of inhibiting undesirable reactions and facilitating sustained synthesis. Herein, it aims to address challenges in electrolytic carboxylation reactions, enhance energy efficiency, analyze reactions using diamond electrodes, ultimately establish a new synthesis method contributing to carbon neutrality.A comparative analysis of BDD and platinum electrodes was conducted to confirm the superior performance of BDD. BDD electrodes were prepared using the microwave plasma chemical vapor deposition method, employing acetone and methanol as carbon sources and boron trioxide as the boron source. Plasma irradiation of a mixture of raw materials and hydrogen gas was used to deposit BDD on a silicon substrate. Prior to the experiment, the BDD surface underwent ultraviolet ozone treatment with oxygen to enhance stability and establish consistent initial conditions. Under N2 or CO2 atmospheric conditions, cyclic voltammetry (CV) was performed with a scanning rate of 10 mV/s in Bu4NBF4/acetonitrile (0.1 M) and acetophenone (0.01 M) to investigate the electrochemical behavior of BDD and Pt electrodes. CV studies were utilized to investigate the reduction potential. Finally, acetophenone was synthesized via constant current electrolysis under a CO2 atmosphere.Figure 1 displays the CV curves of a) BDD and b) Pt electrodes in acetonitrile solvent and acetophenone electrolyte, respectively. In the electrocarboxylation reaction, the electrochemical reduction of acetonitrile and CO2 occurs as a side reaction. Our findings indicate that the reduction of acetonitrile and CO2 does not occur at the reduction potential of acetophenone when using a BDD electrode. Conversely, when a Pt electrode is employed, acetonitrile is slightly reduced by the reduction potential of acetophenone, and CO2 reduction occurs as a side reaction. Figure 2(a) depicts the yield of atrolactic acid obtained using both BDD and Pt electrodes. In case of Pt electrode 13 % yield of atrolactic acid while in case of BDD electrode 25 % yield of atrolactic acid observed. These results demonstrate that the electrocarboxylation reaction efficiency of BDD electrodes is higher than that of platinum electrodes. Figure 2 (b) shows a schematic diagram of the electrocarboxylation reaction. Initially, acetophenone undergoes one electron reduction. The resulting substance reacts directly with CO2 and undergoes further reduction by one electron 2). This study showcases the potential of BDD electrodes for organic synthesis, particularly in the electrolytic carboxylation of acetophenone. References 1) S. Wang, T. Feng, Y. Wang, Y. Qiu, Chem. Asian. J. 17, e202200543 (2022).2) M. A. Stalcup, et al., ACS Sustainable Chem. Eng. 9, 10431-10436 (2021). Figure 1

Control of electron transfer kinetics at boron-doped diamond electrodes by specific surface modification

Electrocatalytic oxidation of ascorbic acid by [Fe(CN) 6] 3−/4− redox couple electrostatically trapped in cationic N, N-dimethylaniline polymer film electropolymerized on diamond electrode

Introduction The reduction of CO2 has attracted considerable attentions since its abundance in atmosphere and large amount of industrial CO2 gas emission. However, the process has so far been difficult because of its high thermodynamic stability of CO2. The high over potential for CO2 reduction promotes hydrogen evolution, which inhibits CO2 reduction process. In our previous work[ 1], electrochemical CO2 reduction was carried out in NaCl and methanol solution and achieved high faradaic efficiency of product using the Boron-doped Diamond (BDD) electrode, which has chemical inertness and wide potential window. Meanwhile, ammonia solution has been known as a strong CO2 absorber with high CO2 loading capacity. Thus, a high concentration of CO2 can be achieved by using this solution. Herein, we performed the study of electrochemical CO2 reduction in aqueous ammonia solution using BDD electrode. Methods The BDD electrode was prepared by depositing BDD film onto a silicon wafer substrate with Microwave Plasma Assisted Chemical Vapor Deposition (MPA-CVD) during 6 hours. The electrochemical measurements were performed in two compartment cells divided by nafion membrane using Pt as counter electrode, Ag/AgCl as reference electrode, and BDD as working electrode. N2 bubbling during 30 minutes followed by CO2 bubbling during 2 hours were carried out everytime before 2 hours electrochemical reduction at potential ranging from -1.2 V to -1.5 V vs. Ag/AgCl. The liquid product was analyzed using GC-MS, and gas products were analyzed using GC with FID/TCD detector. Results and Discussion BDD film was successfully deposited on silicon wafer. The raman spectrum showed sp3 peak at 1332 cm-1. The sp2 peak at 1500 cm-1 was not observed. Characterization of the BDD surface morphology was also carried out using Scanning Electron Microscopy (SEM) and the grain size of BDD was around 4~7 μm. In addition, SEM image showed no change of the BDD surface after more than 30 hours electrochemical reduction. Thus, the high durability of BDD electrode was proved. The great advantage of ammonia solution to absorb CO2 was confirmed by measuring the CO2 concentration in the solution and compared to KOH and NaCl aqueous solution. The highest CO2 concentration was achieved by ammonia solution. The absorbance capacity was also increased with increasing the concentration of ammonia. The products achieved from this reduction process were methanol, CH4, CO, and H2 gas. The maximum amount of methanol production was 0.25 ppm (24% faradaic efficiency) at the potential -1.3 V vs. Ag/AgCl. This faradaic efficiency is based on the 6 electrons involved in the reaction. On the other hand, CH4 and CO produced at low efficiency. Faradaic efficiencies of products at the various potentials are described in Fig. 1. Aqueous ammonia solution, which is used as a supporting electrolyte, reacts rapidly with CO2 to form bicarbonate ion at pH 7~8[ 2]. In our experiment, the pH of the solution was achieved near the value. Therefore, it is assumed that the reduced species are bicarbonate ions. The electrochemical reduction of aqueous ammonium bicarbonate solution was carried out at the potential -1.3 V vs. Ag/AgCl for 2 hours to reveal the mechanism. As the result, the pH of the aqueous ammonium bicarbonate solution was around 7.9 and methanol was achieved as a main product. On the other hand, study about the importance of ammonia was also performed by reducing CO2 gas in KOH and NaCl aqueous solution in the same condition. We assumed that there is important effect of ammonia since high amount of methanol was only achieved by the presence of ammonia in this condition. In addition, reduction on other electrode was performed on glassy carbon electrode as a carbon based electrode. No methanol was analyzed and high amount of hydrogen gas was produced.

<Introduction> It has recently been revealed that oxytocin (OT), a peptide hormone known for its role in lactation and parturition, works as a neurotransmitter as well. Due to a series of findings of positive effects on social behaviors such as trust in human, oxytocin has been of keen interest to neuroscientists. What is required now for further understanding of oxytocin science is a real-time measurement of oxytocin in vivo. On the other hand, in the region where oxytocin is secreted in the hypothalamus, another peptide, vasopressin (VP), is also secreted. Vasopressin is also a nonapeptide with a quite similar structure to oxytocin. Therefore, selective measurement of oxytocin and vasopressin is inevitable. Electrochemical detection allows a real-time measurement in millisecond order with high sensitivity. Compared to conventional electrodes, boron-doped diamond (BDD) electrode has a variety of outstanding properties such as wide potential window and low background current, which have led to a number of reports about sensitive measurement of substances which cannot be detected by other electrodes. Using BDD microelectrodes, in vivomeasurement of biomolecules have been achieved and applied to medical and physiological studies. In addition, surface termination of BDD can be changed from original state (hydrogen termination) to oxygen termination by some oxidation treatment, which enables selective measurement. In the present study, electrochemical detection of oxytocin was investigated using BDD electrodes. Two types of BDD, as-deposited (AD-BDD) and anodically-oxidized (AO-BDD), were used in order to achieve selective measurement. <Experiments> BDD electrodes were prepared by growing polycrystalline BDD thin films on silicon substrates or needle tungsten wires using microwave plasma-assisted chemical vapor deposition (MPCVD) system. Electrochemical measurements were conducted in a three-electrode system with BDD, platinum, and Ag/AgCl (KCl saturated) electrode as a working electrode, counter electrode, and reference electrode, respectively. Phosphate buffer saline (PBS) and Tris buffer were used as buffer solution after adjusted to pH 7.4. Surface transformation of BDD electrodes to oxygen termination was conducted on AD-BDD by means of anodic oxidation of 3.0 V application for 20 minutes in PBS. <Results and discussion>The electrochemical behavior of oxytocin was studied using AD-BDD. Cyclic voltammetry (CV) was performed for 0.1 mM oxytocin in 0.1 M PBS with a scan rate of 100 mV/s. Oxidation peak was observed at 0.7 V (vs. Ag/AgCl). Among the 9 amino acids constructing oxytocin, only tyrosine (Tyr) has been reported to be electrochemically oxidized. Tyrosine also gave oxidation signal at 0.7 V and the shape of voltammogram was quite similar to that of oxytocin. Consequently, it was deduced that oxidation of oxytocin is occurred at tyrosine moiety. When compared to other electrodes, BDD showed 4 times higher signal to background ratio than glassy carbon electrode. No signal was observed in the case of platinum electrode. These results showed that sensitive measurement of oxytocin is possible by using BDD electrode. Since vasopressin also contains tyrosine in its structure, it should show the oxidation signal. CV of vasopressin was compared to that of oxytocin. Exactly the same voltammograms were observed. On the other hand, AO-BDD, which has oxygen-terminated surface, showed apparent difference in voltammograms (Figure). Although the peak potential of vasopressin was maintained at the same position as AD-BDD, oxytocin showed a broad signal shifted to more positive potential region. On-set potential of tyrosine was still higher than that of oxytocin. One possible explanation to the results is the electrostatic interaction between the electrode surface and the molecules. The surface state of AO-BDD rich in C-O functional groups can be expected to have electrostatically negative state. On the other hand, tyrosine is negatively charged, oxytocin is almost neutral, and vasopressin is positively charged in the condition of pH 7.4. These facts and the results of CV well explain the mechanism of electrostatic interaction. Aiming at in vivo and selective measurement, chronoamperometry combined with flow injection analysis (FIA) by BDD microelectrodes was conducted. AD-BDD microelectrode applied at 1.0 V gave high linearity (R2 = 0.994) of the current peaks over the oxytocin concentration range from 0.1 to 10.0 μM with a detection limit of 50 nM (S/N =3). On the other hand, using AO-BDD microelectrode, selective measurement of oxytocin and vasopressin was achieved by the use of applied potential of 0.54 V, which gave the signals of only vasopressin. Consequently, the concentration of oxytocin can be obtained by subtracting the concentration of vasopressin measured on AO-BDD from that of oxytocin + vasopressin measured on AD-BDD. Figure 1

Boron-doped diamond (BDD) has attracted considerable attention as an electrode material used for electrochemical disinfection of wastewater, due to its high oxygen evolution over-potential.[1], [2] This property enables the formation of highly reactive oxygen species (ROS) such as hydroxyl radicals, ozone, and hydrogen peroxide.[3]–[6] Despite the promise of BDD as a liquid disinfection electrode, there is little information in literature that details the optimal conditions for ROS generation. Effects of potential switching for inhibiting fouling of the electrode surface, evolving surface chemistry, and resultant energy efficiency in sanitizing wastewater are not widely reported. Knowledge of these conditions and their liquid disinfection properties would allow production of ROS with higher efficiency and therefore lower cost in real-world applications. The present work investigates the generation of ROS and subsequent liquid disinfection of wastewater using as-grown boron-doped ultrananocrystalline diamond (BD-UNCD) electrodes. Static and potential switching methods of generating ROS are compared to determine their effects on liquid disinfection, chlorine generation, energy expenditure, electrode fouling, and electrode surface chemistry. These results build on an evolving understanding of the electrochemical generation of ROS from BDD electrodes. Our results show that liquid disinfection of diluted wastewater can occur with negligible chlorination and efficient energy expenditure using potential switching methods. Comparison of potential switching to static potential methods show differences in energy expenditure, chlorination, and electrode scaling; as well as time needed for disinfection of liquid waste. It is proposed that the electrogeneration of functional groups at oxidative potentials of BD-UNCD allows for an increased current density during the successive electrolysis at reductive potentials, and that this electrogeneration correlates to an enhanced production of H2O2. Through potential switching, these functional groups can be stabilized and used continuously to more efficiently produce H2O2, and potentially other ROS, when compared to static potential methods at these same potentials by optimizing the applied potentials and duty cycle. Moreover, potential switching has been previously used to inhibit electrode fouling,[7]–[10] which is commonplace in liquid waste sanitation, and therefore offers a practical method for electrochemical disinfection of wastewater in large scale applications.

We describe a sensitive plant monitoring system by the detection of the bioelectric potentials in plants with boron-doped diamond (BDD) electrodes. For sensor electrodes, we used commercially available BDD, Ag, and Pt plate electrodes. We tested this approach on a hybrid species in the genus Opuntia (potted) and three different trees (ground-planted) at different places in Japan. For the Opuntia, we artificially induced bioelectric potential changes by the surface potential using the fingers. We detected substantial changes in bioelectric potentials through all electrodes during finger touches on the surface of potted Opuntia hybrid plants, although the BDD electrodes were several times more sensitive to bioelectric potential change compared to the other electrodes. Similarly for ground-planted trees, we found that both BDD and Pt electrodes detected bioelectric potential change induced by changing environmental factors (temperature and humidity) for months without replacing/removing/changing electrodes, BDD electrodes were 5–10 times more sensitive in this detection than Pt electrodes. Given these results, we conclude that BDD electrodes on live plant tissue were able to consistently detect bioelectrical potential changes in plants.

Introduction Boron-doped diamond (BDD) electrodes have been attracted considerable attention due to their excellent electrochemical properties, such as wide potential window in aqueous solutions, low background current, and high chemical stability, compared with the conventional electrodes. Hence, BDD electrodes have been investigated for many applications, for example, wastewater treatment, electrochemical sensors, and electroorganic synthesis. On the other hand, it is known that electrochemical properties of BDD can be altered by adjusting boron concentration and/or sp2-bonded carbon impurities1. Therefore, the investigation of the correlation between synthetic condition and electrode properties is important to synthesize suitable BDD for each application. In this work, we synthesized and characterized several BDD electrodes with different boron concentration. Experimental BDD films were prepared onto p-type (100) silicon wafer substrates using microwave plasma enhanced chemical vapor deposition method. They were synthesized with various B/C raitos in the feed gas: 0.01%, 0.1%, 0.5%, 1%, and 2%. Boron concentration in the synthesized BDD was estimated by secondary ion mass spectroscopy (SIMS) and glow discharge optical emission spectroscopy (GDOES). The morphologies were observed by scanning electron microscopy (SEM). Structures were characterized by X-ray diffraction (XRD) and Raman spectroscopy. Electrochemical measurements were carried out in a single compartment cell using a conventional three-electrode system: BDD as a working electrode, a Pt wire as a counter electrode, and Ag/AgCl (saturated KCl) as a reference electrode. The potential windows were evaluated by cyclic voltammetry (CV) in an aqueous solution of 0.1 M H2SO4. Before electrochemical measurements, the BDD surface was hydrogenated by hydrogen plasma treatment or oxidized by anodic oxidation treatment. Results and Discussion SIMS and GDOES analysis indicated that actual boron concentration depended almost proportionally on B/C raitos in the feed gas. The SEM images showed that the grain size and thickness of the BDD films gradually decreased with increasing boron concentration. It is assumed that increasing B/C ratios in the feed gas promotes nucleation of diamond but also interferes with the growth of the grains. XRD patterns of all BDD films showed three sharp peaks, corresponding to (111), (220), and (311) diffractions of the diamond cubic structure. The Raman spectra of all BDD films showed the peak of center zone optical phonon of diamond at around 1300 cm−1. Moreover, in the spectra of more than 0.5%BDD films, the two wide bands were observed at around 470 cm−1 and 1220 cm−1, which are usually observed in high doped BDD. On the other hand, it could not be observed sp2-bonded band at around 1500 cm−1. Consequently, it was successful to synthesize BDD films with different boron concentration. From CV measurements in 0.1 M H2SO4, the potential window narrowed with increasing boron concentration after surface oxidation (Fig.). In addition, CV measurements of 1 mM K3[Fe(CN)6] showed the peak-to-peak potential separation increased with decreasing boron concentration. It is suggested that the thickness of the space-charge layer at the BDD surface reduces with increasing boron concentration. In order to give further insights, we are currently investigating the electrode property on CO2 reduction. References (1) T. Watanabe, Y. Honda, K. Kanda, and Y. Einaga, Phys. Status Solidi A 211, 2709 (2014). Figure 1

In recent years, boron-doped diamond (BDD) electrodes have attained great significance and emerged as outstanding potential candidates for electrochemical carbon dioxide (CO2) conversion to valuable products. The features like chemical stability, abundant economical raw material, and long cyclic stability of BDD electrodes made them highly competitive as compared to the conventional metal-based electrodes. However, the direction of research approach is not focused and not adequate for improvement in the design, yield, and selectivity. Most of the countries have targeted the achievement of “net zero”, i.e., utmost removal of CO2 from the atmosphere that has been emitted by human activities within the next decade. In this context, we have reviewed electrochemical CO2 reduction using a diamond electrode. In this mini-review, we used the curated literature available in the CAS content collection to present a systematic analysis of the various approaches applied by scientists on recent developments on BDD electrodes for electrochemical reduction of CO2. More significantly, we wisely addressed the challenges and future perspectives to improve the yield and selectivity of CO2 reduction products as a direction to researchers in this field. Multiple strategies have been discussed allied to tackle the high overpotential and low carbon monoxide yield issues. The review highlights the current status and developments with focus on understanding the reaction mechanisms, impact of dopant concentration on performance, improved electrolyte designs, surface characteristics, choice of electrolytes, and challenges such as low yield and unsatisfactory selectivity of BDD based CO2 electroreduction. Our analysis highlights the latest trends alongside the associated challenges with BDD based CO2 electroreduction and future direction for researchers.

Electrochemical CO2 reduction on sub-microcrystalline boron-doped diamond electrodes

Boron-doped diamond (BDD) electrodes are known to have excellent electrochemical properties, such as wide potential window and low background current, as well as extreme physical/chemical stability. Based on these properties, the BDD electrodes are expected to be used for sensitive electrochemical detection in various research fields including bioelectrochemistry. Usually, BDD electrodes are prepared by deposition of a polycrystalline BDD thin film on a conductive silicon wafer substrate, and thus obtained as an inflexible macro-electrode. In order to expand application fields of BDD electrodes for sensitive electrochemical detection, we have developed screen-printed BDD electrodes and BDD microring electrodes. 1. Screen-printed BDD electrodes Screen-printed BDD electrodes were developed as a low-cost, light-weight, flexible, disposable and sensitive electrochemical electrode. An ink containing BDD powder (BDDP, particle size < 1 μm) and polyester (PES) resin binder was prepared and was subjected to screen printing to obtain a polyimide film-based screen-printed BDD electrode. In comparison with conventional carbon-printed electrode, the BDDP-printed electrode was found to show low background current, leading to large signal-to-background (S/B) ratio. Electrochemical properties of the BDDP-printed electrode was changed drastically by the PES/BDDP ratio of the ink. The BDDP-printed electrode showed planar electrode-type behavior at small PES/BDDP ratios. At a BDDP-printed electrode with large PES/BDDP ratios, however, microelectrode-type voltammetric behavior was observed due to the random microelectrode array effect. The S/B ratio for the voltammetric detection of ascorbic acid was found to be in the order BDDP-printed electrode (PES/BDDP = 1.0) > BDDP-printed electrode (PES/BDDP = 0.3) > conventional polycrystalline BDD electrode. 2. BDD microring electrodes BDD microring electrodes were developed for electrochemical detection at a micrometer-scale local space. A quartz glass rod was pulled to prepare a quartz glass needle with a tip diameter of ca. 200 nm. BDD thin film was deposited on the needle tip to obtain BDD microelectrode. After deposition of an insulating layer on the electrode surface, the tip was cut by focused ion beam to obtain microring electrode. Diameter of the BDD microring electrode was ca. 5 μm. Oxygen reduction reaction current at a platinum microelectrode in the presence of bovine serum albumin (BSA) was found to be reduced by 58% from the current in the absence of BSA. In contrast, the current reduction was found to be 20% at the BDD microring electrode, showing good durability to electrode fouling by the presence of BSA.

Introduction The recovery of Cu from wastewater is a key issue for environmental and economic aspects1. The wastewater treatment containing Cu has been carried out by various techniques such as chemical precipitation, coagulating sedimentation, and electrochemical methods. Although chemical precipitation method is the most commonly used technique due to relatively simple operation, the process needs to put additional chemicals and generates large amounts of sludge. On the other hand, electrodeposition is known as the “clean” method because it is able to achieve the recovery of Cu without requiring addition of chemicals and generating sludge. However, the current efficiency tends to decrease especially in a dilute solution, because hydrogen evolution and oxygen reduction reaction occur as competition reaction. Boron-doped diamond (BDD) electrode is a candidate for resolving the above problem because it has the excellent electrochemical properties2. Along these lines, we study on the recovery of Cu from dilute cupric sulfate solution as a model wastewater by electrodeposition method using BDD electrodes, and glassy carbon (GC) as a comparative carbon electrode. Experimental Two types of BDD films with different boron doping level (B/C = 0.1%, 1%) were deposited onto silicon wafer substrates by a microwave plasma-assisted chemical vapor deposition method. Electrochemical measurements were carried out using a conventional three-electrode system: BDD and GC as a working electrode, Pt plate as a counter electrode, and Ag/AgCl (saturated KCl) as a reference electrode. The surface of BDD electrodes was oxidized in 0.1 M H2SO4 at 2.0 V for 10 min before electrochemical measurements. The electrochemical behavior of Cu ions was evaluated by cyclic voltammetry (CV) in an aqueous solution of 0.5 mM CuSO4 and 0.1 M H2SO4 with a scan rate of 0.3 V s−1. Before CV measurements, the solution was deoxidized by bubbling with nitrogen for 10 min. Electrodeposition of Cu was carried out by chronoamperometry at various potentials from 0 to −0.8 V in 9-ml aqueous solution of 0.5 mM CuSO4 and 0.1 M H2SO4. During the electrodeposition, nitrogen kept bubbling in the solution. After electrodeposition, concentration of residual Cu ions was measured by an inductively coupled plasma atomic emission spectroscopy. Results and Discussion Figure 1 showed the time-dependent Cu recovery rates and current efficiencies at the various potentials on BDD and GC electrodes. When the electrodeposition was carried out at 0 V on all electrodes, Cu could hardly deposit on the electrodes. The Cu recovery rates on 0.1%BDD increased with increasing the applied negative potential, whereas the Cu recovery rates on GC decreased at −0.8 V, compared to the other potentials. On 1%BDD, Cu recovery rates hardly changed at any potential except 0 V. From CV measurements, reduction potentials corresponding to Cu2+ ions to metal Cu were −0.48 V, −0.28 V, and −0.20 V on 0.1%BDD, 1%BDD, and GC, respectively. Since the nucleation potential of Cu on 0.1%BDD is the most negative, Cu recovery rates at −0.2 V was lower than the other potentials. The nucleation overpotentials were different between 0.1%BDD and 1%BDD due to the difference of their conductive properties. As 0.1%BDD has a characteristic of a p-type semiconductor, a depletion layer occurs at the surface of the electrode with a band bending when the electrode contacts the solution. Therefore, cathodic reactions are inhibited due to increasing the depletion layer when applying the negative potential. On the other hand, 1%BDD has a characteristic of metal-like conductivity, so charge transfer from the electrode to Cu ions easily occurs. Also, the hydrogen evolution potential on 0.1%BDD was the most negative, followed in order by 1%BDD, and GC. Therefore, Cu recovery rates at −0.8 V on GC decreased due to the hydrogen evolution. The current efficiencies decreased with increasing the applied negative potentials on the all electrodes, because hydrogen evolution reaction easily occurs at more negative potential. Also, the current efficiencies on BDD were higher than GC at any potential. It is assumed that the current efficiency was improved using BDD electrodes due to inhibition of hydrogen evolution reaction, compared to GC electrode. Moreover, the current efficiency using 0.1%BDD was the higher than 1%BDD due to higher hydrogen overpotential, whereas 0.1%BDD also required high Cu deposition overpotential. Therefore, it was found that the recovery of Cu was achieved with high current efficiency using 1%BDD along with the lower power consumption. References (1) F. Fu and Q. Whang, J. Environ. Manage. 92, 407 (2011). (2) Y. Einaga, J. Appl. Electrochem. 40, 1807 (2010). Figure 1

Converting excessive CO2 molecules into formic acid (HCOOH) as a liquid fuel and hydrogen storage carrier using a sustainable electrochemical method has received enormous attentions. However, the reaction mechanism during this two-electron reaction pathway is still controversial. Inspired by the high selectivity toward HCOOH on the boron-doped diamond (BDD) electrode, this work calculates the adsorption of the CO2 molecule and first two-electron reaction pathway on BDD with different B doping configurations by the density functional theory method. The results show that CO2 molecules are more readily adsorbed on the surface B doping sites with charge transfer between B-O bonding. And the total overpotential of the first two-electron reaction pathway displays a Volcano relationship with the Gibbs energy of the *CO2-*COOH step. The partially sp2-C hybridized (111) (2 × 1) configuration exhibits the lowest overpotential of 0.81 eV and the best CO2 reduction performance toward the HCOOH product. Furthermore, the dynamic kinetics of the *CO2-*COOH step is investigated by the climbing image-nudged elastic band method under the external electric field. The negative electric field of -0.4 eV/Å promotes the adsorption of CO2 and *H but inhibits the migration of *H with an energy barrier of 4.34 eV. This work elucidates the decision factor of high selectivity toward the HCOOH product on the BDD electrode and provides a comprehensive understanding of two-electron reaction pathway mechanisms.

Fosamprenavir is a pro-drug of the antiretroviral protease inhibitor amprenavir and is oxidizable at solid electrodes. The anodic oxidation behavior of fosamprenavir was investigated using cyclic and linear sweep voltammetry at boron-doped diamond and glassy carbon electrodes. In cyclic voltammetry, depending on pH values, fosamprenavir showed one sharp irreversible oxidation peak or wave depending on the working electrode. The mechanism of the oxidation process was discussed. The voltammetric study of some model compounds allowed elucidation of the possible oxidation mechanism of fosamprenavir. The aim of this study was to determine fosamprenavir levels in pharmaceutical formulations and biological samples by means of electrochemical methods. Using the sharp oxidation response, two voltammetric methods were described for the determination of fosamprenavir by differential pulse and square-wave voltammetry at the boron-doped diamond and glassy carbon electrodes. These two voltammetric techniques are 0.1 M H(2)SO(4) and phosphate buffer at pH 2.0 which allow quantitation over a 4 x 10(-6) to 8 x 10(-5) M range using boron-doped diamond and a 1 x 10(-5) to 1 x 10(-4) M range using glassy carbon electrodes, respectively, in supporting electrolyte. All necessary validation parameters were investigated and calculated. These methods were successfully applied for the analysis of fosamprenavir pharmaceutical dosage forms, human serum and urine samples. The standard addition method was used in biological media using boron-doped diamond electrode. No electroactive interferences from the tablet excipients or endogenous substances from biological material were found. The results were statistically compared with those obtained through an established HPLC-UV technique; no significant differences were found between the voltammetric and HPLC methods.

Diamond is grown in some laboratories by either HPHT process or Plasma-Enhanced Chemical Vapor Deposition (MP-CVD) since a few decades. Single crystal diamond exhibits outstanding properties including a high optical transparency over a broad electromagnetic spectrum, high thermal conductivity approx. five times higher than copper, and acoustic wave velocity close to 19 000 m.s-1. It displays also remarkable mechanical properties with e.g. a Young’s modulus exceeding 1000 GPa along with high resistance to fracture, to name a few. Some of these properties remain also remarkable in its polycrystalline form when compare to most other materials. Furthermore, diamond can be doped with nitrogen or boron during growth, offering electrical properties from semiconducting to quasi-metallic regimes. When heavily doped with boron (~2.1021 cm-3), the so-called Boron Doped Diamond (BDD) electrodes become attractive electrodes featuring a high potential window > 3V in water and low double-layer capacitance. Moreover, diamond is extremely resilient to corrosion and more generally to chemical attacks. It is also biocompatible, which makes it very attractive for in-vivo sensing applications. Finally, the carbon nature of the diamond offers wide opportunities for surface grafting of chemical or biochemical functional groups through highly stable covalent carbon-carbon bonding. These properties can be exploited advantageously to enhance the analytical performances and stability of chemical/biochemical sensors and have motivated our research over the last 15 years. Our work focuses mainly on polycrystalline diamond thin films that can be grown typically on inches silicon substrates, thus offering access to some clean-room processes and potentially large-scale production.Several processes were elaborated to micro-pattern diamond layers in order to design chemical transducers such as gravimetric MEMS devices, electrodes, field effect transistors, etc. Diamond microstructures may also be transferred to flexible parylene or polyimide substrates, thus making them attractive e.g. for wearable sensors and implantable medical electrodes. Further techniques have also been developed to enhance the active surface area of diamond transducer surfaces at the nanoscale and thus increase drastically the sensitivity of the resulting sensors by multiplying the number of active sites. Here diamond is typically grown onto well-chosen high aspect ratio templates that can withstand the growth conditions of diamond in high-density hydrogen plasma. Most of these methods have been “standardized”. They involve clean-room processing including dry etching, photolithography, and so on and forth. As examples, heavily doped diamond electrodes were developed successfully both as macro- and micro-electrodes for biomedical, pharmaceutical or foodstuff analysis applications. These applications benefit both from the high analytical performances of diamond electrodes in particular due to their low background signals and high reactivity, and high stability and reliability. BDD electrodes may also be modified with transition metal nanoparticles to enhance their catalytic behavior. From this concept, diamond multi-electrode arrays were designed for chemical patterns identification, for instance for sensory analysis of coffee, or for the monitoring of environmental pollutants. BDD electrodes offer also significant advantages in electrochemiluminescence (ECL) techniques, which are being investigated for various applications ranging from foodstuff analysis to narcotics detection. A key benefit of BDD electrodes for all of the above applications is certainly that they can be electrochemically reactivated following fouling, sometimes directly in the analytical medium, to maintain high reactivity thus opening the way to reusable sensors and online monitoring. Besides, BDD microelectrode arrays have also been transferred to flexible substrates for neural stimulation and recording, along with in-vivo neuromodulators measurements. Finally, diamond based MEMS devices (microcantilevers, SAW sensors) take advantage both of the mechanical properties of diamond, along with steady carbon interface for convenient bio-functionalization. Our work here focused mainly on the detection of odorant molecules, using biomolecular receptors involved in olfaction in Nature as sensitive layers, including Odorant Binding Proteins (OBPs), Major Urinary Proteins (MUPs) and Olfactory Receptors (OR). Multisensor array instrumentations were developed around this concept, for applications ranging from breathe analysis to security applications.