Diamond Cathode Research Articles

Field emission from point diamond cathodes under continuous laser irradiation

The presented study investigates the impact of continuous laser irradiation in the visible range on the field emission properties of diamond needle-like micro-sized crystallites with a nanometer tip radius. The measurements were carried out in a vacuum diode configuration with a flat metal anode using DC voltage source. It was found that the field emission current increased under illumination, showing a direct correlation with the radiation power. At a maximum power density of about 400 W/cm2 the relative increase in current under the action of laser irradiation was 13%. The relative increase in current is determined by the parameters of the dark current-voltage characteristic and reaches its maximum value in the region corresponding to the minimum increase in dark current with voltage. It is shown that the most likely mechanism for the increase in current is a change in the electrical resistance of the diamond microneedle as a result of absorption of laser radiation in the presence of electron levels located in the band gap of the diamond associated with impurities or structural defects in the near surface layer of the diamond microneedle.

Field Electron Emission from Point Diamond Cathodes under Continuous Laser Irradiation

Field Electron Emission from Point Diamond Cathodes under Continuous Laser Irradiation

Solar light-assisted electrochemical CO2 reduction on a boron-doped diamond cathode

Photoelectrochemical water oxidation with a hematite (α-Fe2O3) photoanode and electrochemical CO2 reduction with a boron-doped diamond (BDD) cathode were combined to convert CO2 into formic acid under 1 sun AM 1.5 simulated solar light irradiation.

Anode Reaction Control for a Single-Compartment Electrochemical CO2 Reduction Reactor with a Surface-Activated Diamond Cathode.

The electrochemical reaction of carbon dioxide (CO2 ) in aqueous electrolyte solutions is attracting increasing attention for sustainable chemical production. Boron-doped diamond (BDD) electrodes have been previously shown to be very effective for the stable electrochemical production of formic acid from CO2 . Typically, the electrochemical production of formic acid by CO2 reduction (CO2 R) reaction is performed with a dual-compartment flow reactor equipped with a membrane separator. The problems caused by the membrane separator, such as scaling-up, complicated operational control and materials costs can be solved using a membrane free single-compartment reactor. Here we demonstrate anode reaction control for a single-compartment CO2 R flow reactor using a surface-activated BDD cathode and achieve a Faradaic efficiency for formic acid production of over 70 %.

Removal of pharmaceutical compounds from real urban wastewater by a continuous bio-electrochemical process at pilot scale

A coupled bio-electrochemical treatment was designed by combining a microalgae-based system with an electro-oxidation (EO) process for removing pharmaceutical compounds in real urban wastewater. First, a preliminary study was carried out at bench scale to identify the best configuration for the coupled treatment, which involved determining whether EO should be used as a pre or post-treatment of the microalgae-based system. The results showed that using EO as a post-treatment provided the best removal results for most of pharmaceuticals, with an average of 58.8% compared to 47.7% obtained with EO as a pre-treatment. Based on these results, a bio-electrochemical treatment was designed using a high rate algal pond (HRAP) followed by an EO process at pilot scale. EO process was evaluated using a Boron Doped Diamond electrode anode and cathode (BDD/BDD cell) with a current density of between 20 and 30 mA cm−2 and an electrolysis time of one hour. This coupled treatment showed removal efficiencies above 80% for hypolipidemic, analgesics and anti-inflammatory drugs. However, antiepileptic drugs showed the lowest removal rate between 36.8% and 69.1%. It is noteworthy that carbamazepine and 10,11-Dihydro-10,11-dihydroxycarbamazepine (CBZ-Diol) showed almost five times the removal rate in the coupled treatment compared to HRAP alone. Overall, the coupled bio-electrochemical treatment proved to be efficient in removing the studied pharmaceutical compounds. The HRAP pre-treatment reduced the presence of organic and inorganic load by 77.4%, allowing the EO process to remove the more recalcitrant target contaminants.

Photo-Fenton and Electro-Fenton performance for the removal of pharmaceutical compounds in real urban wastewater

The objective of this study was to evaluate the performance of Photo-Fenton (PF) and Electro-Fenton (EF) processes and find the best option for the removal of pharmaceutical compounds in a real urban effluent of wastewater treated by a chemically-enhanced primary treatment (CEPT). In both processes was used the iron residual (average 2.4 mg L−1) resulting from CEPT avoiding further iron salts addition. Central composite designs (CCD) with response surface methodology (RSM) were applied to select the operational conditions. Humic acid (HA) was the chelating agent in the PF process, where Fe3+:HA molar ratios and H2O2 concentrations were the factors. While current density and the electrolysis time were the factors in the EF process. The operational conditions selected for evaluating the removal of pharmaceutical compounds were a 1:6.8 for Fe3+:HA molar ratio and 100 mg L−1 for H2O2 in PF, and 80 mA cm−2 and 100 min for EF. EF was evaluated with a Boron Doped Diamond electrode anode and cathode (BDD/BDD cell) without the addition of supporting electrolyte. In PF, the removal efficiencies were between 24.2% and 56% for gabapentin, ibuprofen, naproxen, pentoxifylline, and venlafaxine. Compounds such as carbamazepine and fenofibric acid increased their concentration after the PF process. This increase was related to the enzymatic cleavage of glucuronides and the possible presence of •OH radical scavengers that decreased the process efficiency. By contrast, EF showed an average removal efficiency of between 53.3% and 99.9% for all identified compounds, resulting in the best option for treating this real effluent of wastewater. These results in EF could be related to a synergic effect between homogeneous •OH and BDD(•OH) that contributed to improving the oxidation of the contaminants. The electrical energy per order (EEO) was determined with values between 11.5 and 144.9 kWh log−1 m−3, suggesting a need to apply other preliminary treatments that reduce the current density (i.e., coupled treatments with the biological process).

Photo-assisted electrochemical CO2reduction at a boron-doped diamond cathode

A photo-assisted electrochemical system converting CO2into formic acid by photoelectrochemical water oxidation at TiO2nanotubes coupled with electrochemical CO2reduction at boron-doped diamond.

A New Pathway for CO2 Reduction Relying on the Self-Activation Mechanism of Boron-Doped Diamond Cathode.

By means of an initial electrochemical carbon dioxide reduction reaction (eCO2RR), both the reaction current and Faradaic efficiency of the eCO2RR on boron-doped diamond (BDD) electrodes were significantly improved. Here, this effect is referred to as the self-activation of BDD. Generally, the generation of carbon dioxide radical anions (CO2•–) is the most recognized pathway leading to the formation of hydrocarbons and oxygenated products. However, the self-activation process enabled the eCO2RR to take place at a low potential, that is, a low energy, where CO2•– is hardly produced. In this work, we found that unidentate carbonate and carboxylic groups were identified as intermediates during self-activation. Increasing the amount of these intermediates via the self-activation process enhances the performance of eCO2RR. We further evaluated this effect in long-term experiments using a CO2 electrolyzer for formic acid production and found that the electrical-to-chemical energy conversion efficiency reached 50.2% after the BDD self-activation process.

Removal of Bentazone Pesticide from Aqueous Solutions by Electro-oxidation Method

The kinetics of the electro-oxidation degradation of prepared aqueous solutions containing bentazone as a model compound of the thiadiazine group of pesticides was studied in the lab. The oxidation process was conducted under galvanostatic polarization in natural model media using boron-doped diamond (BDD) cathode and anode. Chemical oxygen demand (COD) estimation along the electro-oxidation treatment processing allowed the assessment of kinetic of organic compounds decay as well as the instantaneous current efficiency. The obtained data reflected that the degradation of bentazone pesticide is significantly dependent on initial amount of bentazone pesticide, current density and electrolytes concentration. COD removal follows a pseudo first-order kinetic and the electro-oxidation process was under the control of mass transport within the range studied, regardless the conditions of experimental. The COD removal rate increases with applied current density until 20 mA/cm2 and decreases for higher values. Two different concentrations supporting electrolyte (5mM, 10mM) were used. The rate of degradation increased significantly with increasing electrolyte concentration. The best obtained conditions for COD removal efficiency on the BDD electrode to degrade bentazone solutions (COD= 91.18 %) include operating at 20 mA/cm2 and 10 mM Na2SO4 as supporting electrolyte. This arrangement and condition allow to approximately complete degradation of bentazone in just 80 min. A decrease in the relative toxicity index value along the electro-oxidation indicate toxic compounds disappearance. The initial toxicity EC50 (5 min) and (15min) were decrease by 81% and 94% The kinetics of the electrooxidation degradation of prepared aqueous solutions containing bentazone as a model compound of the thiadiazine group of pesticides were studied in the lab. The oxidation process was conducted under galvanostatic polarization in natural model media using boron-doped diamond (BDD) cathodes and anode. Chemical oxygen demand (COD) estimation along the electro-oxidation treatment processing allowed the assessment of kinetic of organic compounds decay as well as the instantaneous current efficiency. The obtained data reflected that the degradation of bentazone pesticide is significantly dependent on initial amount of bentazone pesticide, current density and electrolytes concentration. COD removal follows a pseudo first-order kinetic and the electrooxidation process was under the control of mass transport within the range studied, regardless the conditions of experimental. The COD removal rate increases with applied current density until 20 mA/cm2 and decreases for higher values. Two different concentration (5mM, 10mM) were used. The rate of degradation increased significantly with increasing electrolyte concentration. The best obtained conditions for COD removal efficiency on the BDD electrode to degrade bentazone solutions (COD= 91.18 %) include operating at 20 mA/cm2 and 10 mM. This arrangement and condition allow to approximately complete degradation of bentazone in just 80 min. A decrease in the value of  relative toxicity index along the electrolysis indicate the disappearance of toxic compounds. The initial toxicity EC50 (5min) and (15min) were reduced by 81% and94% respectively after 80 minutes.

An efficient, formic acid selective CO2 electrolyzer with a boron-doped diamond cathode

A diamond electrode–based CO2 electrolyzer was fabricated. With this electrolyzer, a faradaic efficiency of 96% and electrical-to-chemical energy conversion efficiency of 43% for the production of formic acid can be obtained.

Efficient treatment for textile wastewater through sequential electrocoagulation, electrochemical oxidation and adsorption processes: Optimization and toxicity assessment

In this work, the sequential Electrocoagulation + Electro-oxidation + Activated carbon adsorption (EC + EO + AC) process was studied as an alternative for the treatment of an industrial textile wastewater (TWW) issuing from a manufacturing company located in Medellín (Colombia). The EC's and EO's operational conditions were optimized using a Box-Behnken experimental design, the Response Surface Methodology and a constrained nonlinear optimization algorithm in terms of organic matter degradation efficiency. The best performance for EC (i. e., dye removal = 94%, COD and TOC degradation of 45 and 40%, respectively) was obtained using Fe anode and Boron Doped Diamond (BDD) cathode, with current density, j EC , equals to 5 mA/cm 2 , pH = 9.3, 60 RPM and 10 min of electrolysis. After EC treatment, the effluent biodegradability (evaluated as the BOD 5 /COD ratio) increases from 0.14 to 0.23. Regrettably, EC was not effective for the removal of acute toxicity to Artemia salina since the treated effluent remained very toxic (100%). The treatment of EC's effluent by EO enhanced organic pollutant removal. For EC + EO sequential process, EO optimal operational conditions ( j EO = 10 mA/cm 2 , pH = 3, 240 RPM , BDD as anode and Fe as cathode) allowed reduction of 100% of color, 88% of COD and 79% of TOC after 30 min of electrolysis. Moreover, the BOD 5 /COD ratio increased from 0.23 to 0.58; however, the treated effluent remained very toxic to the Artemia salina . Consequently, an activated carbon adsorption step was included to complete the treatment process. Thus, by coupling the EC + EO + AC process, effluent's acute toxicity decreased completely. From molecular weight distribution analysis, it was concluded that EC + EO was efficient in eliminating low molecular weight (< 5 kDa) compounds. Finally, the operation cost, which includes chemical reagents, electrodes, energy consumption, and sludge disposal, for the EC + EO + AC sequential process was estimated in 3.83 USD /m 3 . Graphical abstract

Aqueous lithium and sodium ion capacitors with boron-doped graphene/BDD/TiO2 anode and boron-doped graphene/BDD cathode exhibiting AC line-filtering performance

This paper reports our investigation of aqueous sodium and lithium ion capacitors (SIC and LIC, respectively) with a boron-doped graphene (BDG)/boron-doped diamond (BDD) cathode and BDG/nanocrystal BDD/TiO2 nanotube array anode. Vertically grown BDG nanosheets formed a porous three-dimensional morphology rich in charge storage sites with a short ion-diffusion distance and, high structural stability. In an aqueous NaCl solution, the potential windows are 0–1.1 V and −1.2–0 V for the cathode and anode, respectively, and their specific capacitances are 66.76 and 23.86 mF cm−2 at a current density of 3 mA cm−2, respectively. The devices exhibit high energy densities (SIC: 47.8 μWh cm−2; LIC: 33.9 μWh cm−2) and high power densities (SIC: 77.7 mW cm−2; LIC: 65.3 mW cm−2) at an operating voltage of 2.5 V. The SIC and LIC exhibited 100% coulombic efficiency over 10,000 cycles, with a capacitance retention of 99.5% and 97.8%, respectively, at a high current density of 90 mA cm−2 over 2000 cycles. Moreover, the capacitors exhibit effective AC current filtering over a wide frequency range of 50–10,000 Hz. The coulombic efficiencies and long-term stabilities of these aqueous devices are better at high current densities, and large energy densities are retained at high power densities, which is advantageous for high-frequency filtering.

Electrochemical treatment for greywater reuse: effects of cell configuration on COD reduction and disinfection byproduct formation and removal

Abstract Electrochemical (EC) treatment presents a low-energy, water-reuse strategy with potential application to decentralized greywater treatment. This study focused on evaluating the impacts of cell configuration, current density, and cathode material on chemical oxygen demand (COD) removal and disinfection byproduct (DBP) formation in greywater. The formation and/or cathodic removal of active chlorine, perchlorate, haloacetic acids, and trihalomethanes were assessed during EC treatment. DBP formation was proportional to current density in undivided EC cells. Sequential anodic-cathodic treatment in divided EC cells resulted in COD removal in the catholyte and anolyte. The anodic COD removal rate (using a mixed metal-oxide anode) was greater than the cathodic removal rate employing boron-doped diamond (BDD) or graphite cathodes, but anodic and cathodic COD removal was similar when a stainless-steel cathode was used. The overall energy demand required for 50% COD removal was 24% less in the divided cells using the graphite or BDD cathodes (13 W-h L−1) compared to undivided cells (20 W-h L−1). Perchlorate formation was observed in undivided experiments (&amp;gt;50 μg/L), but not detected in divided experiments. While haloacetic acids (HAAs) and trihalomethanes (THMs) were generated anodically; they were removed on the cathode surface in the divided cell. These results suggest that divided configurations provide potential to mitigate DBPs in water reuse applications.

Beta Radiation Enhanced Thermionic Emission from Diamond Thin Films

Diamond-based thermionic emission devices could provide a means to produce clean and renewable energy through direct heat-to-electrical energy conversion. Hindering progress of the technology are the thermionic output current and threshold temperature of the emitter cathode. In this report, we study the effects on thermionic emission caused by in-situ exposure of the diamond cathode to beta radiation. Nitrogen-doped diamond thin films were grown by microwave plasma chemical vapour deposition on molybdenum substrates. The hydrogen-terminated nano-crystalline diamond was studied using a vacuum diode setup with a 63Ni beta radiation source-embedded anode, which produced a 2.7-fold increase in emission current compared to a 59Ni-embedded control. The emission threshold temperature was also examined to further assess the enhancement of thermionic emission, with 63Ni lowering the threshold temperature by an average of 58 ± 11 oC compared to the 59Ni control. Various mechanisms for the enhancement are discussed, with a satisfactory explanation remaining elusive. Nevertheless, one possibility is discussed involving excitation of pre-existing conduction band electrons that may skew their energy distribution toward higher energies.

Localizing Holes as Polarons and Predicting Band Gaps, Defect Levels, and Delithiation Energies of Solid-State Materials with a Local Exchange-Correlation Functional

This work assesses the performance of seven exchange–correlation functionals (some with and some without a Hubbard U correction) for their ability (i) to predict band gaps of silicon, diamond, and Li-ion battery cathode materials, (ii) to localize hole polarons and predict delithiation energies in Li-ion battery cathode materials, and (iii) to predict transition levels of charge carriers of doped silicon and diamond. Both local and hybrid exchange–correlation functionals were tested. The local functionals tend to underestimate band gaps and delocalize polarons. The hybrid functionals very often give a good description of both properties, but they may not be practical for calculations involving large unit cells, large ensembles, or dynamics, and therefore a local functional with a Hubbard U correction is often used (giving the method called DFT+U), where the value of a parameter U is adjusted according to the system and the property being investigated. Keeping in mind the importance of computational cost a...

Graphite distributed electrodes for diamond-based photon-enhanced thermionic emission solar cells

Graphite conductive vertical microchannels, fabricated by femtosecond laser treatment, are proposed as distributed electrodes in defect-engineered (“black”) single-crystal diamond cathodes for innovative solar cells. Energy conversion is based on photon-enhanced thermionic emission, where the reduction of the cathode series resistance is crucial to preserve conversion efficiency. Process yield higher than 80% and resistivity as low as 0.75 ± 0.15 Ω cm were achieved by the optimization of laser parameters and the use of a multi-pass writing technique. A 100 × 100 array of graphite electrodes was integrated in a diamond-based cathode prototype, reducing the series resistance of more than 10 orders of magnitude with respect to bulk diamond.

Modeling electron emission and surface effects from diamond cathodes

We developed modeling capabilities, within the Vorpal particle-in-cell code, for three-dimensional simulations of surface effects and electron emission from semiconductor photocathodes. They include calculation of emission probabilities using general, piece-wise continuous, space-time dependent surface potentials, effective mass, and band bending field effects. We applied these models, in combination with previously implemented capabilities for modeling charge generation and transport in diamond, to investigate the emission dependence on applied electric field in the range from approximately 2 MV/m to 17 MV/m along the [100] direction. The simulation results were compared to experimental data. For the considered parameter regime, conservation of transverse electron momentum (in the plane of the emission surface) allows direct emission from only two (parallel to [100]) of the six equivalent lowest conduction band valleys. When the electron affinity χ is the only parameter varied in the simulations, the value χ = 0.31 eV leads to overall qualitative agreement with the probability of emission deduced from experiments. Including band bending in the simulations improves the agreement with the experimental data, particularly at low applied fields, but not significantly. Using surface potentials with different profiles further allows us to investigate the emission as a function of potential barrier height, width, and vacuum level position. However, adding surface patches with different levels of hydrogenation, modeled with position-dependent electron affinity, leads to the closest agreement with the experimental data.

钛基底的纳米金刚石掺混纳米碳管的场发射特性

On the basis of field emission characteristics of nano-diamond,the field emission characteristics of diamond doped CNTs were studied. The composite coating of diamond and CNTs was formed using electrophoretic deposition,and the cathode samples were fabricated after heat treatment. The microstructure,field emission and luminescence performance of the samples were characterized. Compared with the undoped diamond cathode,the turn-on field of the composite coating cathode decreases obviously,the field emission current increases. The fluorescent powder on the anode surface can luminescent under lower electric field,but the luminescence is nonuniform and the phenomena of ‘edge luminescence'occurs. The improvement of the field emission characteristics is due the enhancement of the electron transportation capacity of the composite coating and the increase of the effective emitter number. Finally,the reasons of ‘edge luminescence'were explained.

纳米金刚石掺混纳米氧化锌的场发射特性

Chrysanthemum-like Zinc Oxide(ZnO)nanorods was fabricated and characterized by hydrothermal route,the diamond was mixed to prepare electrophoretic fluid.After electrophoretic fluid was dispersed by ultrasonic cleaning machine,the coatings were deposited on titanium substrates.Field emission characteristics were tested after heat treatment.Results show that turn-on field of undoped diamond cathode is 7.3V/μm and field emission current density is 81μA/cm2 when electric field is set at20V/μm,while the doped samples show low turn-on field of 4.7~6.0V/μm and high field emission current density of 140~158μA/cm2.The reason is that after the interfusion of nano-ZnO,the electron transport capacity of coating is enhanced,the number of effective emitters increase and field enhancement factorβis improved.Because of diamond,the good bonding between coating and substrate is guaranteed after heat treatment and ohmic contact is formed,which reduces the thermal effect of field emission current.The stability of field emission current declines with the increasing amount of mixed ZnO.Both field emission current density and its stability should be considered,so mixing an appropriate amount of ZnO with nano-diamond can effectively improve field emission characteristics.

Application of Photoelectro-Fenton/BDD Process Based on the Cathodic Production of H2O2 for Degradation of Industrial Dyes

Photoelectro-Fenton/BDD process promotes in situ hydrogen peroxide (H2O2) by means of oxygen reduction via two electrons, adding Fe2+ to the solution resulting in the production of free hydroxyl radicals (•OH). The reaction can be catalyzed by the UV ligth accelerating the degradation of organic compounds in solution, because it promotes the photocehmical regeneration of Fe2+, and as a result a major •OH radicals production. In the present work, the authors discussed the study of the H2O2 production over boron doped diamond (BDD) cathode and the degradation of two industrial azo dyes, Blue-BR (B-BR) and Black-TRS (B-TRS) by photoelectro-Fenton/BDD (PEF/BDD) process using UV-ligth source. Comparative electrolyses carried out with 3L filter press pilot plant equipped with a BDD anode and cathode at constant current density showed the superiority of the processes with BDD because of the higher oxidation ability of ·OH formed from water oxidation at the BDD surface. Total mineralization was rapidly reached for the most potent treatment of PEF with BDD due to the additional oxidation by ·OH produced from Fenton's type reaction between added Fe2+ (0.5mM) and H2O2 generated at the cathode. Azo dyes decay always followed a pseudo-first-order kinetics. The influence of current density and substrate concentration on PEF with BDD was examined.