13 research outputs found
Hydroxide Ion Oxidation in Aqueous Solutions Using Boron-Doped Diamond Electrodes
The
electrochemical oxidation behavior of hydroxide ions at the
surface of boron-doped diamond (BDD) electrodes is presented. The
hydroxide ion oxidation behavior was found to be affected by the surface
conditions of the BDD electrode. Over the NaOH concentration range
of 0.5–10 mM, a well-defined voltammetric wave attributed to
hydroxide ion oxidation was observed at ∼1.25 V versus a Ag/AgCl
reference electrode when using an anodically oxidized BDD (AO-BDD)
electrode, while it was observed at around ∼1.15 V when a cathodically
reduced BDD (CR-BDD) electrode was used. Although the hydroxide ion
oxidation profiles were slightly different for the AO-BDD and CR-BDD
electrodes, the peak currents was each found to have linear relationships
with the NaOH concentration over the same range
Hydroxide Ion Oxidation in Aqueous Solutions Using Boron-Doped Diamond Electrodes
The
electrochemical oxidation behavior of hydroxide ions at the
surface of boron-doped diamond (BDD) electrodes is presented. The
hydroxide ion oxidation behavior was found to be affected by the surface
conditions of the BDD electrode. Over the NaOH concentration range
of 0.5–10 mM, a well-defined voltammetric wave attributed to
hydroxide ion oxidation was observed at ∼1.25 V versus a Ag/AgCl
reference electrode when using an anodically oxidized BDD (AO-BDD)
electrode, while it was observed at around ∼1.15 V when a cathodically
reduced BDD (CR-BDD) electrode was used. Although the hydroxide ion
oxidation profiles were slightly different for the AO-BDD and CR-BDD
electrodes, the peak currents was each found to have linear relationships
with the NaOH concentration over the same range
Sluggish Electron Transfer of Oxygen-Terminated Moderately Boron-Doped Diamond Electrode Induced by Large Interfacial Capacitance between a Diamond and Silicon Interface
Boron-doped diamond (BDD) has tremendous potential for
use as an
electrode material with outstanding characteristics. The substrate
material of BDD can affect the electrochemical properties of BDD electrodes
due to the different junction structures of BDD and the substrate
materials. However, the BDD/substrate interfacial properties have
not been clarified. In this study, the electrochemical behavior of
BDD electrodes with different boron-doping levels (0.1% and 1.0% B/C
ratios) synthesized on Si, W, Nb, and Mo substrates was investigated.
Potential band diagrams of the BDD/substrate interface were proposed
to explain different junction structures and electrochemical behaviors.
Oxygen-terminated BDD with moderate boron-doping levels exhibited
sluggish electron transfer induced by the large capacitance generated
at the BDD/Si interface. These findings provide a fundamental understanding
of diamond electrochemistry and insight into the selection of suitable
substrate materials for practical applications of BDD electrodes
Long-Term Continuous Conversion of CO<sub>2</sub> to Formic Acid Using Boron-Doped Diamond Electrodes
The
long-term durability of boron-doped diamond electrodes (BDD)
used continuously in the electrochemical conversion of CO<sub>2</sub> to formic acid was investigated. Although the Faradaic efficiency
(FE) for the production of formic acid decreased with increasing electrolysis
time, the FE was easily recovered by electrochemical oxidation of
the BDD electrodes in H<sub>2</sub>SO<sub>4</sub>, Na<sub>2</sub>SO<sub>4</sub> or K<sub>2</sub>SO<sub>4</sub> solutions. For practical application,
the long-term production of formic acid using BDD electrodes can be
successfully accomplished just by successive polarity reversal of
plus and minus terminals. Furthermore, at a current density of −20
mA cm<sup>–2</sup>, the rate of production reached 328 μmol
h<sup>–1</sup> cm<sup>–2</sup>, which is the highest
value ever obtained using plate electrodes. Consequently, we found
that BDD electrodes are ideal for industrial application of CO<sub>2</sub> reduction
First Principles Calculation Study on Surfaces and Water Interfaces of Boron-Doped Diamond
We investigated water interfaces
of boron-doped diamond (BDD) terminated by hydrogen, oxygen, and hydroxyl
groups by using density functional theory (DFT)-based molecular dynamics
to elucidate the electrochemical behaviors of the as-grown and oxidized
BDD electrodes. The reversible outer-sphere electron transfer on the
as-grown electrode and the irreversibility on the oxidized electrode,
observed in the experiment, are well explained by the BDD band position
and subsurface band bending, which depend on the termination and interfacial
dipoles. The reductive character of the H-terminated BDD is found,
while the interface covered by the carbonyl oxygen is clearly oxidative.
The redox character of the hydroxyl termination depends on the lateral
hydrogen bonding network among the termination groups and is rather
oxidative at the water interface. We also examined the preference
of the boron position in the diamond and the stability of boron pairs
and clusters. It is suggested that the wide distribution of the single
boron dopants is crucial to the BDD conductivity, against the tendency
of clustering. These results give novel atomistic aspects of the termination
and the boron doping effects on the BDD electrodes, which is useful
for further exploration of the efficient electrochemical applications
of BDD
A Study on Electrolytic Corrosion of Boron-Doped Diamond Electrodes when Decomposing Organic Compounds
Electrolytic
corrosion of boron-doped diamond (BDD) electrodes after applying a
high positive potential to decompose organic compounds in aqueous
solution was studied. Scanning electron microscopy images, Raman spectra,
and glow discharge optical emission spectroscopy revealed that relatively
highly boron-doped domains were primarily corroded and relatively
low boron-doped domains remained after electrolysis. The corrosion
due to electrolysis was observed especially in aqueous solutions of
acetic acid or propionic acid, while it was not observed in other
organic compounds such as formic acid, glucose, and methanol. Electron
spin resonance measurements after electrolysis in the acetic acid
solution revealed the generation of methyl radicals on the BDD electrodes.
Here, the possible mechanisms for the corrosion are discussed. Dangling
bonds may be formed due to abstraction of OH groups from C–OH
functional groups by methyl radicals generated on the surface of the
BDD electrodes. As a result, the sp<sup>3</sup> diamond structure
would be converted to the sp<sup>2</sup> carbon structure, which can
be easily etched. Furthermore, to prevent electrolytic corrosion during
electrolysis, both the current density and the pH condition in the
aqueous solution were optimized. At low current densities or high
pH, the BDD electrodes were stable without electrolytic corrosion
even in the acetic acid aqueous solution
Co-reactant-on-Demand ECL: Electrogenerated Chemiluminescence by the in Situ Production of S<sub>2</sub>O<sub>8</sub><sup>2–</sup> at Boron-Doped Diamond Electrodes
A novel <i>co-reactant-free</i> electrogenerated chemiluminescence
(ECL) system is developed where RuÂ(bpy)<sub>3</sub><sup>2+</sup> emission
is obtained on boron-doped diamond (BDD) electrodes. The method exploits
the unique ability of BDD to operate at very high oxidation potential
in aqueous solutions and to promote the conversion of inert SO<sub>4</sub><sup>2–</sup> into the reactive co-reactant S<sub>2</sub>O<sub>8</sub><sup>2–</sup>. This novel procedure is rather
straightforward, not requiring any particular electrode geometry,
and since the co-reactant is only generated in situ, the interference
with biological samples is minimized. The underlying mechanism is
similar to that of the RuÂ(bpy)<sub>3</sub><sup>2+</sup>/S<sub>2</sub>O<sub>8</sub><sup>2–</sup> system; however, the intensity
of the emitted signal increases linearly with [SO<sub>4</sub><sup>2–</sup>] up to ∼0.6 M, with possible implications
for analytical uses of the proposed procedure
Boron-Doped Diamond as a Quasi-Reference Electrode
As
a working electrode, boron-doped diamond (BDD) has been studied
in detail in electrochemical processes because of its superior electrochemical
properties. However, these characteristics have rarely been mentioned
when BDD is used as a quasi-reference electrode (QRE). Herein, we
conducted a systematic investigation on BDD electrodes, with different
boron-doping levels (1 and 0.1%) and different surface terminations
(hydrogen and oxygen) for their application as a QRE. A BDD electrode
with 1% boron and a hydrogen-terminated surface achieved the best
stability. Its open-circuit potential (OCP) exhibited less than 100
mV of potential drift over 6000 s and showed a minuscule half-wave
potential difference (E1/2) of 0.0037
V in 0.1 mM K3[Fe(CN)6]/1 M KCl solution before
and after the OCP measurement. Based on these observations, anions
are found to contribute to the potential, which we preliminarily speculate
as related to the capacitance caused by electrostatic adsorption on
the positively charged hydrogen-terminated surface. The repeatability
of measurement was verified through continuous cyclic voltammetry
tests in 0.1 mM K3[Fe(CN)6]/1 M KCl, showing
a maximum E1/2 difference of 0.042 V.
The contribution of the redox couples was excluded, and the repeatability
was considered to originate from its surface stability. Finally, a
linear response of the optimized BDD as a QRE was validated (R2 > 0.99) by determination of free chlorine
and dopamine concentrations, respectively. These results consolidate
the existing fundamental research on BDD electrodes and promote the
possibility of its application as a QRE in harsh environments or in vivo biological monitoring
Surface Hydrogenation of Boron-Doped Diamond Electrodes by Cathodic Reduction
Boron-doped
diamond (BDD) has attracted much attention as a promising
electrode material especially for electrochemical sensing systems,
because it has excellent properties such as a wide potential window
and low background current. It is known that the electrochemical properties
of BDD electrodes are very sensitive to the surface termination such
as to whether it is hydrogen- or oxygen-terminated. Pretreating BDD
electrodes by cathodic reduction (CR) to hydrogenate the surface has
been widely used to achieve high sensitivity. However, little is known
about the effects of the CR treatment conditions on surface hydrogenation.
In this Article, we report on a systematic study of CR treatments
that can achieve effective surface hydrogenation. As a result, we
found that the surface hydrogenation could be improved by applying
a more negative potential in a lower pH solution. This is because
hydrogen atoms generated from protons in the CR treatment contribute
to the surface hydrogenation. After CR treatments, BDD surface could
be hydrogenated not completely but sufficiently to achieve high sensitivity
for electrochemical sensing. In addition, we confirmed that hydrogenation
with high repeatability could be achieved
Facet-Dependent Temporal and Spatial Changes in Boron-Doped Diamond Film Electrodes due to Anodic Corrosion
The progression of
corrosion in polycrystalline boron-doped diamond
(BDD) thin film electrode is explored as the electrode undergoes high-current
density anodic treatments with organic compounds. Micro-Raman spectroscopy
and spectral mapping indicate that anodic corrosion is initiated by
the conversion of sp<sup>3</sup> diamond to amorphous sp<sup>2</sup> carbon at the surface, which are then removed after longer anodic
treatment. Polarized Raman analysis reveals that corrosion-induced
changes on the surface are specific to (100)-grain facets and (111)-grain
edges. X-ray photoelectron spectroscopic measurements suggest that
carbonyl groups consequently form on these specific sites and act
as an intermediate toward the etching of the surface. This process
exposes and subsequently removes the subsurface boron atoms, thus
reducing the doping density. The observed crystal grain orientation
dependence of the corrosion process provides new insights toward a
better understanding of degradation in BDD electrodes