Boron-doped Diamond Surface Research Articles

Electrochemical Carboxylation: Green Synthesis of Atrolactic Acid Using Boron-Doped Diamond Electrodes

Electrochemical CO2 fixation is vital for sustainability in the chemical industry, yet the selective synthesis of multi-carbon products remains challenging. Organic electrosynthesis offers promise by enabling precise control over reaction conditions and facilitating novel reactivity patterns. One such technique, electrochemical carboxylation, involves coupling CO2 with organic molecules to produce carboxylic acids. Specifically, electro-carboxylation of acetophenone yields atrolactic acid, a valuable precursor for nonsteroidal anti-inflammatory drugs, providing a greener alternative to traditional production methods. This study focuses on the synthesis and characterization of boron-doped diamond (BDD) films using the microwave plasma-assisted chemical vapor deposition (MP-CVD) method and synthesized BDD electrodes were then used for the electrolytic carboxylation of acetophenone. Various analytical techniques, including X-ray diffraction (XRD), Raman spectroscopy, and laser microscopy, etc. were employed to characterize the BDD films. Various BDD films synthesized for different durations were utilized in the electrolytic carboxylation of acetophenone, with the highest yield of atrolactic acid (25%) achieved using a BDD film synthesized over 6 hours. Also, the effect of BDD surface modification i.e. oxygen and hydrogen terminated BDD on the synthesis of atrolactic acid. Additionally, different electrolytes were employed in the synthesis process of atrolactic acid. A comparative study between Pt and BDD electrodes for the electrolytic carboxylation of acetophenone was conducted, and a mechanism for the formation of atrolactic acid was proposed.

Ni-Pt Core-Shell Formation via Spontaneous Galvanic Displacement Reaction at Boron Doped Diamond Electrodes for Ammonia Oxidation Reaction

Ammonia is a major environmental pollutant that is highly toxic and may cause unfavourable effects to the human body, even in low concentrations. As a result, the monitoring and elimination of NH3 has been an important topic worth exploring in depth. Moreover, ammonia can be a suitable fuel cell source because its theoretical electrical charge density is relatively high and it’s possible to take this advantage by converting ammonia to nitrogen and electrical energy via the ammonia oxidation reaction (AOR). This reaction requires a catalyst to decrease the energy barrier that prevents the molecule from reacting and transforming into nitrogen.Ammonia electro-oxidation reaction has been paid much attention in recent years because it is widely used in various fields. However, the electro-oxidation of ammonia is a complex process, especially the reaction intermediate has a slow toxic effect on the electrode. To reduce the catalyst poisoning by the absorption of intermediate, the constituent and structure of the catalysts must be deeply researched.Herein, a bimetallic Pt–Ni catalyst-modified boron-doped diamond (BDD) electrode was done via spontaneous galvanic displacement reaction for the ammonia oxidation reaction. The synergistic properties may include the promotion of low-temperature oxidation, improvement of the oxidation resistance, and increased catalytic efficiency. BDD was used as the electrode substrate in this work due to its excellent resistance to corrosion and good stability over time in a highly corrosive environment. First, nickel was electro-deposited through chronoamperometry on the BDD electrode surface at a potential of -1.1V vs Ag/AgCl in 0.1M KClO4 & 5mM Ni (NO3)2.6H2O aqueous solution. Second, platinum was deposited on the nickel particles on the BDD electrode surface through a spontaneous galvanic displacement reaction by a redox process which involves the nickel oxidation and Pt2+ reduction, using a K2PtCl4 precursor on the BDD surface while forming a core shell structure. Lastly, the Pt-Ni deposited on the BDD surface was then characterized through different techniques such as XPS, SEM, EDS, and Raman before and after the ammonia oxidation reaction.Preliminary studies of the behaviour of BDD electrodes in the presence of Ni and Pt have been carried out to determine the electrochemical conditions at which the substrate works with these metal salts. The results found with these studies will show how Pt-Ni catalyst will improve AOR in alkaline media.

What Are the Key Factors for the Detection of Peptides Using Mass Spectrometry on Boron-Doped Diamond Surfaces?

We investigated the use of boron-doped diamond (BDD) with different surface morphologies for the enhanced detection of nine different peptides by matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS). For the first time, we compared three different nanostructured BDD film morphologies (Continuous, Nanograss, and Nanotips) with differently terminated surfaces (-H, -O, and -F) to commercially available Ground Steel plates. All these surfaces were evaluated for their effectiveness in detecting the nine different peptides by MALDI-MS. Our results demonstrated that certain nanostructured BDD surfaces exhibited superior performance for the detection of especially hydrophobic peptides (e.g., bradykinin 1-7, substance P, and the renin substrate), with a limit of detection of down to 2.3 pM. Further investigation showed that hydrophobic peptides (e.g., bradykinin 1-7, substance P, and the renin substrate) were effectively detected on hydrogen-terminated BDD surfaces. On the other hand, the highly acidic negatively charged peptide adrenocorticotropic hormone fragment 18-39 was effectively identified on oxygen-/fluorine-terminated BDD surfaces. Furthermore, BDD surfaces reduced sodium adduct contamination significantly.

Binder-free nickel/boron-doped diamond film electrodes for hydrogen evolution reaction in alkaline medium: Effect of nickel catalyst nanostructure on electrochemical performance

Boron-doped diamond (BDD) is a robust electrode material, and Ni metal is a promising alternative electrocatalyst to noble metals for promoting the hydrogen evolution reaction. In this study, binder-free Ni/BDD film electrodes, with Ni acting as a catalyst, were constructed. With thermal annealing temperature regulation, the Ni catalyst exhibited different nanostructures, including amorphous continuous films, partially crystalline corrugated films, and uniformly dispersive nanoparticles. The electrodes were characterized via scanning electron microscopy, grazing-incidence X-ray diffraction, and X-ray photoelectron spectroscopy. Furthermore, the impact of the Ni catalyst fine structure on the hydrogen evolution reaction performance was evaluated. The results highlighted the versatility of BDD as a platform for developing binder-free Ni/BDD electrodes. Through precise adjustment of the nano-scale structure of Ni catalysts on the BDD surface, high hydrogen evolution reaction activity was achieved, with an overpotential as low as 273 mV at 10 mA/cm2 in a 1 M KOH solution.

Advanced electrochemical detection of arsenic using platinum-modified boron-doped diamond by anodic stripping voltammetry

Background: Platinum-modified boron-doped diamond (BDD) electrodes were effectively fabricated through a combination of wet seeding and electrodeposition techniques. Methods: This research involved the utilization of various chemicals and apparatus, the modification of boron-doped diamond (BDD) electrodes with platinum using wet seeding and electrodeposition, and the detection of As3+ and As5+ using a phosphate buffer solution and anodic stripping voltammetry (ASV). Findings: Characterization using Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS) confirmed the successful deposition of 1.54% platinum on the BDD surface. These modified electrodes were employed as sensors for arsenic species (As³⁺ and As⁵⁺) using anodic stripping voltammetry (ASV) in a 0.1 M phosphate buffer solution at pH 6. Under optimal conditions, including a deposition potential of -500 mV, a deposition time of 150 s, and a scan rate of 200 mV/s, the linear detection of As³⁺ and As⁵⁺ was achieved within a concentration range of 0 to 100 ppb (R² = 0.9797 and 0.9903, respectively). Prior to ASV detection of As⁵⁺, a pretreatment step involving the addition of 0.1 M NaBH₄ was necessary to reduce As⁵⁺ to As³⁺. The detection limits for As³⁺ and As⁵⁺ were determined to be 16.50 ppb and 8.19 ppb, respectively. Conclusion: This research highlights the potential of BDD/Pt electrodes in environmental monitoring and arsenic detection applications and demonstrates the method's efficacy for the speciation analysis of arsenic species. Novelty/Originality of this Study: This research pioneers the use of platinum-modified boron-doped diamond electrodes for the speciation analysis of arsenic, offering a promising new approach for environmental monitoring applications.

Highly Sensitive and Selective Detection of L-Tryptophan by ECL Using Boron-Doped Diamond Electrodes.

L-tryptophan is an amino acid that is essential to the metabolism of humans. Therefore, there is a high interest for its detection in biological fluids including blood, urine, and saliva for medical studies, but also in food products. Towards this goal, we report on a new electrochemiluminescence (ECL) method for L-tryptophan detection involving the in situ production of hydrogen peroxide at the surface of boron-doped diamond (BDD) electrodes. We demonstrate that the ECL response efficiency is directly related to H2O2 production at the electrode surface and propose a mechanism for the ECL emission of L-tryptophan. After optimizing the analytical conditions, we show that the ECL response to L-tryptophan is directly linear with concentration in the range of 0.005 to 1 µM. We achieved a limit of detection of 0.4 nM and limit of quantification of 1.4 nM in phosphate buffer saline (PBS, pH 7.4). Good selectivity against other indolic compounds (serotonin, 3-methylindole, tryptamine, indole) potentially found in biological fluids was observed, thus making this approach highly promising for quantifying L-tryptophan in a broad range of aqueous matrices of interest.

Enhanced electrochemical ozone production via sp2 carbon content optimization in boron doped diamond electrodes using laser micromachining

The role and bonding arrangement of deliberately added sp2 carbon in maximising the current efficiency, output and longevity of boron doped diamond (BDD) electrodes for electrochemical dissolved ozone generation is elucidated. We show, using a zero-gap cell (ZGC) arrangement, how systematically increasing sp2 carbon results in increased ozone concentration and current efficiency. sp2 carbon addition is made using nanosecond pulse laser micromachining which converts BDD to sp2 carbon. Two ZGC geometries are investigated which both incorporate a Nafion membrane sandwiched between two BDD electrodes. Through-holes (perforations) are integrated into either the membrane or the BDD, the latter using laser micromachining which also converts the hole walls to sp2 carbon. Increasing the number of through-holes (or changing hole geometry), in the perforated BDD, increases the sp2 carbon content of the electrode (from 5 to 100 %). For the perforated Nafion membrane in contact with a planar BDD electrode, patterned laser micromachining of the BDD surface is used to control the sp2 carbon content of the electrode (from 4 to 100 %). For both electrodes, sp2 carbon content is significantly higher than is possible using diamond growth. sp2 carbon contents >40 % and >60 % for the planar and perforated BDD electrodes, respectively, are found to be particularly effective, allowing electrode designs to be proposed for optimised ZGC ozone generation. Notably, the sp2 carbon introduced via laser micromachining is shown to be extremely stable over 20 h (anode potential ∼ 10 V) in contrast to glassy carbon, which corrodes within 10 min. Whilst both are 100 % sp2 carbon, the laser-machined surface (after ozonolysis) is amorphous whereas the glassy carbon contains disorganized graphitic layers. This work also highlights the intriguing stability of amorphous sp2 carbon towards high oxidative potentials.

Influence of gas adsorption on surface potential of porphyrin functionalized boron doped diamond thin films

Porphyrins functionalized diamond surfaces are interesting candidates for wide variety of applications due to their remarkable physical and chemical properties. In this work, the properties of 5-(4-carboxyphenyl) triphenyl porphyrins functionalized boron-doped diamond (BDD) surface followed by gas adsorption were studied at room temperature. After structural and morphological characterizations of the bare BDD surface and porphyrins functionalized BDD surface, a scanning Kelvin probe system was used to investigate the surface potential distribution due to the adsorption of volatile organic compounds (VOCs) under visible light illumination conditions. Gas adsorption studies showed poor response in bare BDD surfaces under different gas atmospheres. On the other hand, a significant response with discriminable gas interactions was achieved in porphyrins functionalized BDD surface under visible light illumination. The obtained results suggest that visible light has influenced gas interactions because of porphyrins. The increased response (∼ 2.5 times) of metal-free porphyrin functionalized BDD thin film towards triethylamine (TEA) is accounted to the donor nature of TEA. This study helps in developing a new generation of novel conductive type diamond-based photo enhanced gas sensors at room temperature that can be utilized for fish freshness monitoring.

Unravelling microstructure-electroactivity relationships in free-standing polycrystalline boron-doped diamond: A mapping study

In this work, four different techniques were concurrently applied to study the interplay between local electroactivity and electrode surface characteristics of free-standing, polycrystalline boron-doped diamond (BDD). Scanning electron microscopy, electron back-scatter diffraction, Raman mapping and scanning electrochemical microscopy were used to probe the electrode morphology, grain orientation and boundaries, composition, and local electrochemical activity, respectively. Both nucleation and growth BDD surfaces together with the cross-section area were carefully investigated for the first time in a single study using the combination of all four techniques. This enabled us to obtain significant insights into the highly heterogeneous nature of the polycrystalline BDD material. Notably, boron dopants were confirmed to be non-uniformly distributed over the BDD material, which is characterized by a distinct columnar structure and composition of grains of various orientations. Particularly, the highest electrochemical activity was recorded on the highest doped (111) crystal orientation. In contrast, the averagely boron-doped (100)-oriented facet showed non-conductive nature. This highlights that the local electrochemical activity of the BDD surface is strongly grain-dependent and the most significant factors governing the obtained responses are crystallographic orientation and boron doping. Moreover, increased boron and sp2 carbon content in the boundary regions was recognized by Raman mapping. However, such localized enrichment in impurities did not translate into enhanced electrochemical activity, which implies that boron atoms at the inter-grain areas are predominantly inactive. Finally, it is crucial to consider all characteristics of the polycrystalline BDD including crystal orientation, which is particularly relevant if micro- and nanoscale probing is intended.

Synthesis of gold nanoparticles with allicin to modify boron-doped diamond surface for oxygen sensor applications

Modification of surface of boron-doped diamond (BDD) film with gold nanoparticles (AuNPs) was carried out to increase its catalytic activity for an application as an oxygen sensor. Allicin was isolated from garlic by salting out extraction technique, and then used as the capping agent to synthesize AuNPs as it has a double bond structure that could be reacted to attach the BDD surface under UV light radiation. An average size of AuNPs at around 46,00 ± 9,06 nm was obtained, while the modification of the BDD surface by the synthesized AuNPs indicated that the surface of BDD could be covered by gold at around 0.6 % (w/w). Investigation of the AuNPs-modified BDD as a working electrode for the oxygen reduction by using cyclic voltammograms in 0.1 M phosphate buffer solution pH 7 observed a current peak at around -0.45 V (vs. Ag/AgCl). The current of this peak linearly increased proportionally to the dissolved oxygen concentrations (R2=0.9986). Moreover, a limit of detection of the dissolved oxygen of 0.12 ppm and limit of quantity 0.41 ppm could be achieved with excellent stability at 6.86% RSD with 6 repetitions and sensitivity at 19.086 μA/ppm indicated that the modified BDD is promising for applications as an oxygen sensor.

Electroreduction of CO2 into CO Using Amine-Modified Diamond Electrode

Electroreduction of CO2 is promising to convert CO2 into value-added compounds since electroreduction does not necessarily require a catalyst because an electrochemical energy itself can activate the reactivity of CO2. Most of the reported studies on CO2 electroreduction use a metal electrode material, and the selectivity of reduction products depends on the metal species. However, as the use of noble or toxic metals should be avoided from the viewpoint of sustainability, a metal-free carbon-based material are desirable. Along these lines, we have focused on boron-doped diamond (BDD) as a carbon-based electrode in CO2 electroreduction. On the other hand, molecular modification of electrode surface is an important technique in various fields. Functional molecules can be covalently immobilized onto carbon electrodes by an electrografting method. Along these lines, we decided to immobilize amine on BDD surface, which integrates CO2 capture and storage technologies and CO2 electroreduction. Here, we prepared amine-modified BDD (NH2-BDD) to elucidate an effect of amine modification on CO2 electroreduction.Prior to the electrolysis experiments, linear sweep voltammetry (LSV) was performed to investigate the electrochemical difference between bare- and NH2-BDD. As an energetically equivalent criterion for the CO2 electroreduction, E red was defined as the potential at which the current density reached -30 µA/cm2; E red (vs. Ag/AgCl) were determined to be -1.56 and -1.16 V for bare-BDD and NH2-BDD, respectively. A positive shift of E red in the NH2-BDD electrode is probably because CO2 molecules form the C-N bond with the amino group on the electrode surface, which results in enhancing the electrophilicity of the carbon atom. Next, we investigated how amine modification affects the product selectivity in CO2 electroreduction. Products were CO, HCOOH, and H2 regardless of the type of electrode and applied potentials. Difference between the Faraday efficiencies (FE) of HCOOH and CO production was dependent on applied potentials in NH2-BDD. Particularly, in the most prominent case, the selectivity of CO production was 8 times higher for NH2-BDD than the case of bare-BDD. Since CO production requires the adsorption of intermediate species, CO2 • -, on the electrode surface, the adsorption of CO2 and CO2 • - would be promoted on NH2-BDD through the formation of C-N bond. In order to obtain the direct evidence for CO2 capturing by NH2-BDD during the electroreduction, in situ ATR-IR measurements were performed. We focused on the C=O (carbonyl) stretching vibration of the carbamate anion, observed in the region of 1700-1500 cm-1. In NH2-BDD, a broad peak attributed to the C=O stretching vibration was observed at around 1640 cm-1, and the peak intensity decreased as the applied potential became negative. This result strongly supports that CO2 was captured by amine at the BDD surface to form the carbamate anion and reduced to CO.The above discussion can be explained by the behavior of LSV of NH2-BDD, in which two drops were observed. The first drop at around -1.20 V (vs. Ag/AgCl) is probably ascribed to the reduction of CO2 captured by amine, and the second drop at around -1.70 V (vs. Ag/AgCl) is ascribed to the reduction of free CO2. Therefore, CO production would be favored at potentials between -1.20 and -1.70 V (vs. Ag/AgCl) and HCOOH production would be favored at potentials more negative than -1.70 V (vs. Ag/AgCl). These threshold potentials are in good agreement with the potentials at which the product selectivity switched. It is noted that, in bare-BDD electrodes showing the different E red, the selectivity of CO production was almost unchanged, which suggests that the potential dependence of product selectivity in CO2 electroreduction cannot be explained only by differences in E red. Therefore, the product selectivity was driven by the interaction between the surface amine groups and CO2, i.e. the reaction via carbamate formation. Figure 1

Can HOCl be superficially stabilized on an electrocatalyst as proposed in the active chlorine mechanism involving •OH radicals?: Beyond the Cl2 evolution

According to Comninellis’ proposal on water oxidation, anodes physisorbing active oxygen readily form •OH radicals to develop electrocombustion processes, while electrode surfaces forming the so-called higher oxide MO x+1 chemisorb active oxygen, being more prone to perform the O2 evolution reaction (OER). Here, we adopt a similar premise to account for the active chlorine mechanism (ACM), assuming that the capacity of an electrocatalyst to physisorb/chemisorb active oxygen determines the type of chlorine species formed and stabilized. Density Functional Theory (DFT) calculations are conducted to evaluate the stability of HOCl, OCl and OCl --H+ species oxidant species on Boron Doped Diamond (BDD), and rutile-type surfaces (110 plane) of SnO2, TiO2, PbO2, RuO2, and IrO2, in the absence and presence of H2O molecules. The computed relaxed models reveal that SnO2 and PbO2 physisorbing active oxygen are only able to stabilize OCl-ads species on pentacoordinated transition metal atoms (M5c); whereas RuO2, and IrO2 chemisorbing active oxygen produce Clads- on an adjacent M5c active site. The BDD surface is the only surface able to maintain the HOCl stability with and without H2O solvation. Thus, it is proposed that BDD and TiO2, physisorbing active oxygen, preferentially adopt a 2-electron transfer step to generate (HOCl)ads; while SnO2 and PbO2, with moderate physisorption, also follow a 2-electron transfer step but produced (OCl-)ads and (H+)ads, thus dissociating (HOCl)ads. RuO2 and IrO2, preferentially forming the so-called higher oxide MOx+1, adopt a 3-electron transfer step to either produce (OCl)ads, or (O)ads + (Cl)ads, where there is a more equal competition towards the oxygen evolution.

(Invited) Structure and Dynamics of Interfacial Species in Electrical Double Layer

Understanding electrochemical processes is of importance for many industrial and scientific fields. Especially, interfacial species, such as electrolyte ions and solvent significantly affect electrochemical reaction activity. Surface oxide species also promote or inhibit various electrode reactions; therefore, the oxidation processes of metal electrode have been investigated using in situ vibrational spectroscopy. Infrared (IR) spectroscopy is an important tool because it can detect the complementary vibrational modes of surface oxide species. However, observation of the low-frequency mode is restricted by infusible IR windows such as CaF2, that are generally used in the IR reflection absorption spectroscopy (IRAS). We developed a complementary IR method that can be used to avoid contamination by dissolved ions from window material. The fusible low-pass IR window can be applied to in-situ IRAS measurements [1,2]. The adsorbed hydroxide was observed on the single crystal Pt electrodes depending on the surface orientation, its coverage was correlated with the decrease in oxygen reduction reaction activity [3]. Recent time resolved X-ray diffraction measurements revealed that there is a delay in the approach of alkali metal cations to surface because the interfacial water causes a blocking effect [4]. Therefore, the kinetics of approaching step in the EDL is significantly different from that of migration in the bulk phase, and the adsorption rate depends on the hydration structure, ionic valence, and ionic size. Although X-ray diffraction provides a distribution of interfacial species, it does not provide sufficient information about species identification and molecular orientation. We investigated the coadsorption dynamics of metal cation and (bi)sulfate anion using time resolved IR measurement [5]. Boron doped diamond (BDD) is a promising material of which properties are significantly different from those of metals and other carbon materials. However, the complex atomic arrangement and oxidation state of the polycrystalline BDD surface inhibit an atomic level study on the relationship between the electrochemical response and surface structure. More detailed surface analyses are necessary for the investigation of the electrode surface of BDD. We applied in situ ATR−IR spectroscopy to reveal the oxidative species and dopamine oxidation on the BDD electrode [6,7].[1] M. Nakamura, Y. Nakajima, N. Hoshi, H. Tajiri, O. Sakata, ChemPhysChem, 14, 2426 (2013).[2] M. Nakamura, Y. Nakajima, K. Kato, O. Sakata, N. Hoshi, J. Phys. Chem. C, 119, 23586 (2015).[3] T. Kumeda, H. Tajiri, O. Sakata, N. Hoshi, M. Nakamura, Nat. Commun., 9, 4378 (2018).[4] M. Nakamura, H. Kaminaga, O. Endo, H. Tajiri, O. Sakata, N. Hoshi, J. Phys. Chem. C, 118, 22136 (2014).[5] M. Nakamura, T. Banzai, Y. Maehata, O. Endo, H. Tajiri. O. Sakata, N. Hoshi, Sci. Rep., 7, 914 (2017).[6] T. Ogose, S. Kasahara, N. Ikemiya, N. Hoshi, Y. Einaga, M. Nakamura, J. Phys. Chem. C, 122, 27456 (2018).[7] R. Hosoda, N. Kamoshida, N. Hoshi, Y. Einaga, M. Nakamura, Carbon, 171, 814 (2021).

Stability of Single Gold Atoms on Defective and Doped Diamond Surfaces.

Polycrystalline boron-doped diamond (BDD) is widely used as a working electrode material in electrochemistry, and its properties, such as its stability, make it an appealing support material for nanostructures in electrocatalytic applications. Recent experiments have shown that electrodeposition can lead to the creation of stable small nanoclusters and even single gold adatoms on the BDD surfaces. We investigate the adsorption energy and kinetic stability of single gold atoms adsorbed onto an atomistic model of BDD surfaces by using density functional theory. The surface model is constructed using hybrid quantum mechanics/molecular mechanics embedding techniques and is based on an oxygen-terminated diamond (110) surface. We use the hybrid quantum mechanics/molecular mechanics method to assess the ability of different density functional approximations to predict the adsorption structure, energy, and barrier for diffusion on pristine and defective surfaces. We find that surface defects (vacancies and surface dopants) strongly anchor adatoms on vacancy sites. We further investigated the thermal stability of gold adatoms, which reveals high barriers associated with lateral diffusion away from the vacancy site. The result provides an explanation for the high stability of experimentally imaged single gold adatoms on BDD and a starting point to investigate the early stages of nucleation during metal surface deposition.

Enhancement of the Catalytic Effect on the Electrochemical Conversion of CO2 to Formic Acid Using MXene (Ti3C2Tx)-Modified Boron-Doped Diamond Electrode

The rising concentration of carbon dioxide (CO2) as one of the greenhouse gases in the atmosphere is a major source of worry. Electrochemical reduction of CO2 is one of many ways to convert CO2 gas into usable compounds. An electrochemical technique was applied in this study to reduce CO2 using a boron-doped diamond (BDD) working electrode modified with MXene (Ti3C2Tx) material to improve electrode performance. MXene concentrations of 0.5 mg/mL (MXene-BDD 0.5), 1.0 mg/mL (MXene-BDD 1.0), and 2.0 mg/mL (MXene-BDD 2.0) were drop-casted onto the BDD surface. MXene was effectively deposited on top of the BDD surface, with Ti weight loads of 0.12%, 4.06%, and 7.14% on MXene-BDD 0.5, MXene-BDD 1.0, and MXene-BDD 2.0, respectively. The modified working electrode was employed for CO2 electroreduction with optimal CO2 gas aeration. The existence of the MXene substance in BDD reduced the electroreduction overpotential of CO2. For the final result, we found that the MXene-BDD 2.0 electrode effectively generated the most formic acid product with a maximum reduction potential as low as −1.3 V (vs. Ag/AgCl).

Electrochemical surface rehydrogenation of boron-doped diamond electrodes after electrochemical polishing

Non-diamond carbon impurity and surface roughness are features that can affect the response of boron-doped diamond (BDD) electrodes. Herein, we report on the electropolishing of BDD electrodes carried out in the presence of acetic and sulfuric acid for different times (1, 2, and 4 h). The wet electrochemical treatment smooths the polycrystalline diamond surface and reduces the non-diamond sp2 carbon impurity content while increasing the surface oxygen content. Changes in surface texture and microstructure were revealed by atomic force microscopy, Raman spectroscopy, and cyclic voltammetry. Subsequently, the surface oxygen content was reduced by increasingly severe cathodic pretreatments (CPTs). This was revealed by changes in the voltametric response for the [Fe(CN)6]3−/4– and ascorbic acid (AA) redox systems, as both exhibit electron transfer kinetics sensitive to the level of oxidation of the BDD surface. For [Fe(CN)6]3−/4–, greater ∆Ep values were obtained for the electropolished (EP-BDD) electrodes, as compared to the as received (AR-BDD) electrode. However, after CPTs the EP-BDD electrodes exhibited smaller ∆Ep values (∼60 mV), which indicate significantly improved electrochemical reversibility and faster electron-transfer kinetics caused by the decreased level of surface oxidation (greater hydrogenation). The increased surface oxygen content brought on by the electropolishing process had also a significant effect on the AA oxidation peak potential (Eap), making it at least ∼140 mV more positive than that for the AR–BDD electrode. However, after CPTs the Eap values for the EP–BDD electrodes became at least ∼0.1 V less positive than that for the AR–BDD electrode, indicating that the surface of the EP-BDD electrodes possesses less surface carbon‑oxygen functional groups (i.e., it is more hydrogenated). The combination of electropolishing and cathodic pretreatment is a way to process the BDD electrode surface to create a smoother, low oxygen surface in much the same way as a hydrogen plasma treatment does.

Flexible boron-doped diamond spiral electrode for application in brain–computer interface based on steady-state visual evoked potential

We propose a flexible boron-doped diamond (BDD) spiral electrode for electroencephalography (EEG) recording and introduce the application of a flexible BDD-based EEG cap in brain–computer interfaces (BCI). The B-doping difference of diamond crystal planes in flexible polycrystalline BDD electrodes makes them act like a microelectrode. Hydrogen bonds between hydroxy fatty acid in the cuticle and BDD surface terminal and electrostatic adsorption between BDD-boron sites and the cuticle enhance the capacitive electric field. Combining a skin-conformal BDD electrode cap with the simplest feature extraction and classification coding can record highly stable EEG in steady-state visual evoked potential (SSVEP), with a high average SNR of 8.6 dB. The BCI system demonstrated competitive accuracy and information transfer rate in five channels in the occipital and parietal areas. Collectively, the BDD-based SSVEP-BCI system offers unique advantages for the real-time monitoring of brain signals, neurological rehabilitation, and disease diagnosis.

Electrochemical reduction of carbon dioxide to acetic acid on a Cu-Au modified boron-doped diamond electrode with a flow-cell system.

Boron-doped diamond (BDD) was modified with copper and gold particles by using an electrodeposition technique to improve its catalytic effect on CO2 reduction in a flow system. The system was optimized based on the production of formic acid by the electroreduction process. At the optimum applied potential of -1.0 V (vs. Ag/AgCl) and flow rate of 50 mL min-1, the copper-gold-modified BDD produced formic acid at the highest rate of 4.88 mol m-2 s-1 and a concentration of 15.93 ppm, while acetic acid was produced with a rate of 0.11 mol m-2 s-1 and a concentration of 0.47 ppm. An advantage of the flow system using the modified BDD was that it was found to accelerate the production rate of acetic acid as well as to decrease the reduction potential of CO2. Furthermore, better stability of the metal particles was observed when using mixed copper-gold modification on the BDD surface than single modification by either metal. The results indicated that a flow system is suitable to be employed for electroreduction of CO2 using the bimetal-modified BDD electrodes, especially with copper and gold as the modifying particles.

Amination of Boron-Doped Diamond Surfaces

Amination of Boron-Doped Diamond Surfaces

Inconsistency of BDD reactivity assessed by ferri/ferro-cyanide redox system and electrocatalytic degradation capability

Ferri/ferro-cyanide ([Fe(CN)6]3−/4−) redox couple has been extensively used as a benchmark to assess electrocatalytic degradation capability of boron-doped diamond (BDD) electrodes. However, the [Fe(CN)6]3−/4− is far more sensitive to the surface terminal groups of BDD surface than the other factors (e.g. surface morphology and electrode configuration) that are closely related to electrocatalytic degradation properties. Thus, inconsistency exists while correlating the degradation properties of BDD with electrochemical properties determined from ferri/ferro-cyanide redox couple. Herein, an exemplar pollutant, reactive blue 19 (RB-19), was electrochemically degraded using various terminated BDD electrodes, including hydrogen-terminated (H-BDD), oxygen-terminated (O-BDD) and porous oxygen-terminated BDDs (OE-BDD), obtained via cathodic and anodic polarization as well as oxygen plasma etching, respectively. Surprisingly, OE-BDD with the lower heterogeneous electron transfer rate constant for [Fe(CN)6]3−/4− showed a better electrocatalytic degradation capability toward RB-19, indicating the inconsistency for qualitatively evaluating degradation properties according to the kinetic parameters extracted from [Fe(CN)6]3−/4− redox system.