We report electrochemical detection of single-catalase collisions at diamond ultramicroelectrodes and show the operative mechanism involves direct enzyme-mediated charge transfer between electrode and solution. Hydrogen peroxide increases the collision frequency, which fluorescence correlation spectroscopy diffusion measurements suggest stems from an increase in the diffusion rate as the underlying cause.

•Hydrogen terminated boron doped diamond (HBDD) is reported as catalyst support.•Electrochemical modification of HBDD with palladium-tin nanoparticles is described.•Synergy between Sn and Pd enhances ethanol electrooxidation and poisoning effects.The modification of hydrogen terminated boron-doped diamond (HBDD) electrode with pure palladium (Pd) and Pd-Sn (tin) nanoparticles is described in this study. For synthesis of Sn/HBDD and Pd-Sn/HBDD electrode, a potentiostatic two-step electrochemical method involving the electrodeposition of Sn followed by Pd was used, respectively. The modification of the HBDD electrode with Sn and noble metal Pd by forming bimetallic Pd-Sn nanoparticle leads to a higher electrocatalytic activity. The electrocatalytic activity of the bimetallic Pd-Sn nanoparticles was evaluated towards the electrooxidation of ethanol in alkaline media and compared with that of the Pd nanoparticles alone. The bimetallic Pd-Sn nanoparticles modified HBDD electrode exhibits higher current densities and less poisoning effects during ethanol electrooxidation compared to Pd/HBDD. The proper tuning of the Pd loading on a foreign metal along with the surface termination effects of the BDD electrode plays a crucial role in achieving a high mass (4.26 × 106 mA/g) and specific (12.37 mA/cm2) electrocatalytic activity of Pd towards ethanol electrooxidation. The aforementioned catalysts of this research possess a high poisoning resistance (If/Ib = 1.63) and stability towards ethanol electrooxidation in alkaline media.Download high-res image (240KB)Download full-size image

In this work, we describe three simple modifications to carbon electrodes that were found to improve the detection of an exemplar neurotransmitter (dopamine) in the presence of physiological interferents (ascorbic acid and/or uric acid). First, the electro-oxidation of ascorbic acid, as a pretreatment, at boron-doped diamond electrode (BDE) interfaces is studied. This treatment did suppress the detection of ascorbic acid oxidation signal, but only in a manner suitable for single-use detection of high concentrations of dopamine (i.e., > 1 μM). Second, the hydrogenation of BDE by electrochemical cathodic treatment and plasma hydrogenation was investigated. Large cathodic, applied potentials (i.e., > – 5 V) and hydrogen plasma pretreatment of BDE lead to the partial and complete oxidization of ascorbic acid before dopamine, respectively. The consequence at hydrogen-plasma treated BDE is the complete electrochemical separation of these two species without any typical catalytic reactions between the analytes. Third, the modification of glassy carbon electrodes with carbon black nanoparticles is explored. This modification enables the simultaneous detection of ascorbic acid, dopamine and uric acid, significantly enhancing the sensitivity of dopamine. Dopamine was best detected using the unconventional route of detecting 5,6-dihydroxyindole, which is made possible by use of carbon-black nanoparticles. The potential of all three studied modifications to be of electroanalytical use is highlighted throughout this work.Keywords: carbon black; diamond; dopamine; electrochemistry; neurotransmitters

Diamond electrochemistry using planar macroscopic diamond films has been widely investigated. Due to the non-uniform doping in diamond, boundary effects, and the varied ratios of graphite to diamond, such systems only provide averaged electrochemical signals over the full electrode. To clarify electrical and electrochemical properties of diamond at the nanoscale, the use of diamond nanostructures (e.g., nanotextures, nanowires, networks, porous film, nanoelectrodes, etc.) and particles (e.g., undoped nanoparticles, boron-doped particles), is highly important. In this review, recent progress and achievements concerning diamond nanoelectrochemistry are considered. After a brief introduction of synthetic strategies to form diamond nanostructures and particles, their electrochemical properties in the presence and absence of redox probes are shown, followed by their use in electroanalysis (e.g., electrochemical, biochemical sensing, etc), electrochemical energy storage (e.g., electrochemical capacitors, batteries, etc.), electrocatalysis, and related applications. Topical problems and future of diamond nanoelectrochemistry are discussed.

Supercapacitors are becoming important energy storage devices in efficient electrical systems and they are typically fabricated from high surface area carbon materials which are manufactured using complex, eco-destructive processes. An alternative approach is based on the conversion of biomass materials which we explore in this paper. Cellulose from cotton pulp is subject to a two-step carbonisation process at a range of elevated temperatures up 1900 °C. The resultant materials are characterized using a range of physical methods, along with cyclic voltammetry and galvanostatic discharge techniques to measure the specific capacitance of the materials formed. It is shown that the optimum processing temperature is around 1000 °C; at lower processing temperatures, the materials are insufficiently conductive whilst at high carbonization temperatures low capacitance is seen due to a loss of surface area. This arises from the inaccessibility of nanometre size pores which are present in abundance after the lower temperature carbonization steps. Cotton pulp carbonised at 1000 °C showed the highest value of capacitance of 107 F g−1 with excellent stability for 2000 cycles. The electrochemical performance of this material is very competitive to other reported carbon materials and indicates the two-stage carbonisation method described is suitable for converting biomass into high quality carbon-based materials for supercapacitor applications.

•A simple scalable fabrication process to generate Si-based powders in the absence of oxide passivating layers is developed.•The material reacts spontaneously with water to produce hydrogen in high yield.•In combination with water the material this represents a viable fuel to generate hydrogen on demand for fuel cell uses.The development of a safe technique for the supply of hydrogen to small portable fuel cells has emerged as a significant barrier to their deployment in recent years, with solutions centering on the use of hydrogen absorption materials, or the generation of hydrogen through chemical reaction. In the present work we demonstrate that the ball-milling of Si under inert conditions in the presence of KOH and sucrose results in the formation of a fine Si-based powder which reacts spontaneously with water at ambient starting temperature to evolve hydrogen rapidly at high yield. Embedded KOH is capable of accelerating the hydrolysis reaction of silicon by the self-heating effect attributed to dissolution heat of KOH, obviating the need for external heating to initiate the reaction; it also reduces the sensitivity of the reaction to oxide contamination of the Si surface by enabling its dissolution in the form of soluble silicates. Moreover, the silicon–water reaction can be switched on and off by adjusting the ambient temperature. It is shown that ball-milled, KOH-embedded Si powder is able to react with different water sources, such as tap water, river water, and salt water, to produce H2 under aerobic conditions. The method represents a cheap scalable approach for the safe provision of hydrogen fuel to small fuel cells.Download high-res image (154KB)Download full-size image

The electrochemical detection of H2O2 using boron doped diamond electrode modified by silver nanoparticles and haemoglobin is reported. Silver nanoparticle obtained from electrodeposition in the presence of cetyl hexadecylthmoniom bromide (CTAB) surfactant shows the best combination of detection limit, sensitivity and reproducibility. The presence of Ag nanoparticles helps bind haemoglobin to the electrode in an active form, leading to a significantly further increase of electrode response to H2O2. Detection limits below 1 μM are achieved by a synergistic effect of both modifiers, and a good linear signal response is seen up to 8 mM. Interferences from glucose, uric acid, ascorbic acid and dopamine at typical physiological levels are shown to be negligible.

The preparation of nanostructured diamond electrodes, decorated with Pt nanoparticles is described in this work. The method involves the electrodeposition of Pt particles on the diamond electrode surface, after which the structure is treated with either an oxygen plasma or an hydrogen plasma. In the former treatment, the Pt particles serve as a hard resist during the oxygen plasma etching of the diamond, yielding structures consisting of Pt particles located on the top of diamond nanorods. In the latter treatment, the Pt catalysed gasification of diamond in the hydrogen plasma occurs, leading to the localisation of the Pt particles in nanopits on the electrode interface. The electrochemical activity of this latter structure with regard to the electrochemical oxidation of both glucose and methanol is demonstrated. It is shown that the hydrogen plasma treatment provides a viable route for the preparation of Pt decorated electrodes with significantly improved chemical stability.

•A novel route to prepare dispersed Pt nanoparticles on conductive diamond supports is identified.•The method uses a combination of electroless and electrolytic reactions.•Highly dispersed, adherent Pt nanoparticles are distributed evenly over the support.•A significant advance towards diamond supported catalysts for fuel cell application is achieved.A novel electroless deposition method was demonstrated to prepare a platinum electrocatalyst on boron doped diamond (BDD) substrates without the need for pre-activation. This green method addresses the uniformity and particle size issues associated with electrodeposition and circumvents the pre-activation procedure which is necessary for conventional electroless deposition. The inert BDD substrate formed a galvanic couple with an iron wire, to overcome the activation barrier associated with conventional electroless deposition on diamond, leading to the formation of Pt nanoparticles on the electrode surface in a galvanic process coupled to a chemical process. When sodium hypophosphite was employed as the reducing agent to drive the electroless reaction Pt deposits which were contaminated with iron and phosphorus resulted. In contrast, the reducing agent ascorbic acid gave rise to high purity Pt nanoparticles. Optimal deposition conditions with respect to bath temperature, pH value and stabilizing additives are identified. Using this approach, high purity and uniformly distributed platinum nanoparticles are obtained on the diamond electrode surface, which demonstrate a high electrochemical activity towards methanol oxidation.

The use of a zirconia thin layer coating to attach phosphate terminated DNA oligonucleotides to a diamond electrode was explored. This DNA functionalised electrode shows an enhanced redox response to the redox mediator methylene blue, which is quenched in the presence of complementary DNA oligonucleotides, enabling the highly sensitive and selective detection of such species in solution. The study shows that the electrodeposition of zirconia on diamond electrodes can be used as an effective and easily implemented route for surface functionalisation and biosensor fabrication using this electrode material.Highlights► A new route to bond ssDNA to diamond electrodes is demonstrated. ► The method utilises electrolysis to deposit a zirconia film. ► An electrochemical biosensor to detect DNA hybridisation is thus demonstrated. ► An accessible route to diamond surface functionalisation is identified.

The dependence of the electrocatalytic properties of Pt–Ru alloy nanoparticles supported on boron-doped diamond electrodes, on the electrodeposition conditions used to prepare them with respect to the oxidation of methanol was studied. Routes involving sequential and simultaneous deposition of the two elements were studied, and the effect of deposition potential was also examined. The morphology of the electrodeposits was characterized by scanning electron microscopy, and shows spherical Pt–Ru nanoparticles for simultaneous deposition and a dendritic structure for sequential deposition. The Pt–Ru binary catalysts from both deposition methods exhibit higher electrocatalytic activity than Pt alone. However, deposits from simultaneous deposition show higher chemical stability and catalytic activity for methanol oxidation than those prepared using sequential deposition, for which significant electrodissolution of Ru is a problem. The optimal Pt:Ru ratio in simultaneous deposition is seen for intermediate deposition potentials. The different morphologies and microstructures for the two deposition methods are also reflected in differing rate-determining steps for methanol oxidization as judged from Tafel analysis. Overall, a sensitive dependence of catalytic properties on electrodeposition parameters is indicated.Graphical abstractElectrochemically deposited Pt-Ru clusters exhibit cyclic voltammetry that is dependent on particle geometry as imaged by electron microscopy.Research highlights► We prepare PtRu nanoparticle clusters on diamond by electrodeposition routes. ► Sequential deposition of the two elements is compared with a simultaneous deposition route. ► Sequential deposition produces a dendritic structure which is unstable because of loss of Ru. ► Simultaneous Pt and Ru electrodeposition gives the best electrocatalyst for methanol oxidation.

The preparation of Pt-modified diamond electrodes by electrodeposition is known to be hampered by poor particle adhesion and a lack of uniformity in the spatial distribution of the deposit over the electrode surface. Here we demonstrate the results can be improved significantly if the electrode is given a simple ultrasonic treatment in the presence of diamond powders prior to electrodeposition. An improvement in spatial distribution and a higher Pt dispersion are seen and, especially, a greater Pt particle stability is observed. Application of these Pt modified diamond electrodes in the electrochemical oxidation of hydrogen peroxide is demonstrated.

The permselective properties of stable opal films formed by polystyrene nanospheres on boron-doped diamond (BDD) electrodes were studied for the first time by means of electrochemical voltammetric and impedance techniques. Films formed from spheres with a diameter above 200 nm are highly porous and have little influence on electrochemical properties. In contrast, porous films formed from 50 nm spheres have a selective influence on the electrochemistry observed, providing an enhancement in the redox peak current for neutral (ferrocenemethanol, dopamine) and positively-charged redox probe mediators (Ru(NH3)63+) and suppressing the current due to a negatively-charged redox species Fe(CN)64−. This is because the latter is repelled from the film, whereas the former are selectively partitioned within it. Partition coefficients, film permeability and diffusion coefficients of species within the polystyrene opal layer are determined. It is shown that a Langmuir isotherm analysis for adsorption on the polystyrene sphere surface can describe successfully the incorporation of ferrocenemethanol and Ru(NH3)63+ within the thin film, with Gibb's free energies (ΔG°) of adsorption in the range of −27 to 28 kJ mol−1. Apart from influencing the magnitude of the detected electrochemical response, it is also shown the opal film increases the resistance to electrode fouling by the reaction products formed by the oxidation of dopamine. Electrochemical impedance measurements further illustrate the effects of the polystyrene layer.

The fabrication of ultramicroelectrodes (UMEs) for analytical electrochemical applications has been explored, using boron-doped diamond as the active electrode material in an insulating coating formed by deposition of electrophoretic paint. Because of the rough nature of the diamond film, the property of such coatings that is normally exploited in the fabrication of UMEs, namely the tendency to retract automatically from sharp protrusions, cannot be used in the present instance. Instead focused ion beam (FIB) sputtering was employed to controllably produce UMEs with well-defined geometry, critical dimension of a few micrometers, and very thin insulating coatings. If the FIB machining is carried out at normal incidence to the diamond electrode surface, significant ion beam damage reduces the yield of successful electrodes. However, if a parallel machining geometry is employed, high yields of ultramicroelectrodes with a flat disk geometry can be obtained very reliably. The electrochemical properties of diamond UMEs are characterized. They show much lower background currents than the equivalent Pt or carbon fiber electrodes but more varied electrochemical response than macroscopic diamond electrodes.

The hot filament chemical vapour deposition of boron-doped diamond was optimised for the fabrication of diamond ultramicroelectrodes. Applications of ultramicroelectrodes require thin, conformal and non-porous diamond coatings, which display electrochemical properties similar to those associated with good quality doped diamond electrodes. The growth conditions to attain these goals are elucidated. The influence of the use of nanodiamond ultrasonic seeding prior to growth, in order to promote nucleation, and varying the negative electrical bias and methane concentration during growth, to control the growth chemistry, are explored. Although Raman spectroscopy shows a deterioration of diamond phase quality with increased negative bias voltage during growth, cyclic voltammetry indicates an improved electrochemical performance due to decreased porosity at reduced grain size under moderate bias voltage. At even higher bias voltage, the electrochemical properties deteriorate due to aggregation of sp2 hybridised carbon at grain boundaries. By combining efficient nucleation methods and appropriate methane concentrations and electrical bias during growth, small grain polycrystalline diamond coatings can be obtained, which show optimal electrochemical properties most suitable for ultramicroelectrode applications.

The first studies are reported on the characteristics of ultra-violet transmissive mode, CVD diamond photocathodes, in which photoelectrons are emitted from a diamond membrane via the opposite interface from that of the incident radiation. For membranes in the thickness range 5–40 μm, the transmissive photoyield at threshold wavelengths is shown to be less but comparable to that measured for reflective, thick film diamond photocathodes. The characteristics are found to be insensitive to the phase purity of differing diamond membranes used, but are very dependent on whether the growth or substrate interfaces of the diamond membrane face the incident UV radiation. The factors influencing the characteristics observed are discussed.

Electrochemical processes, which underlie the use of conductive diamond electrodes for the simultaneous detection of two or more metal ions in solution by anodic stripping voltammetry (ASV), have been investigated. The model analyte system studied contains the two metal species, Ag+(aq) and Pb2+(aq), and the experimental techniques employed include cyclic and square wave voltammetries, along with X-ray photoelectron spectroscopy and secondary electron microscopy. Although the bulk metallic forms of Ag and Pb are immiscible, several interactions in the system between the two metal species present are observed, which significantly influence the electrodeposition and electrodissolution processes which underlie ASV. The subsequent nucleation and growth of a given metal on the electrode surface is enhanced by the presence of the second metal on the surface. The encapsulation of one metal by the other, within the metal particulates that form on the electrode surface, significantly reduces the stripping yield at the potentials characteristic of the individual metals. The stripping potentials are also influenced by bonding interactions between deposited Ag and Pb, which broaden the characteristic stripping peaks in cyclic voltammetry, as well as producing underpotential deposition and stripping. Given these interactions, the extent to which ASV at diamond electrodes can be used to determine the solution concentrations of Ag+(aq) and Pb2+(aq) is considered.

The performance of UV diamond photocathodes in gaseous environments has been explored with regard to the potential applications, which exist for such devices. Stable performance is exhibited even at gas pressures approximately 0.5 bar for hydrogenated diamond, in gaseous environments such as He, H2, O2, CH4 and CF4. However, for chlorocarbon gases, UV stimulated photodissociation of the ambient gas causes the adsorption of chlorine on the diamond surface, and rapidly degrades device performance. Thermal dissociation of ambient gases brings about a similar effect. Thus, although diamond photocathodes do have potential use in gaseous environments, it is clear that care is required to ensure that the hydrogenated surface layer is not destroyed when in use.

Variations in photoyield at 186 and 252 nm have been measured from CVD diamond photocathode materials grown on silicon substrates, as the growth conditions and surface termination were changed. The photoyield increased rapidly for short growth times when the surface comprised a mixture of diamond and non-diamond phases in intimate contact, but this increase occurred at both wavelengths, so poor spectral selectivity resulted. Further growth caused the photoyield to decay as the diamond content of the film improved, before rising again at longer growth times, whence improved wavelength discrimination was also observed. Caesiation enhanced the photoyield observed compared to hydrogenated interfaces.

Abrasive stripping voltammetry, using chemical vapour deposition (CVD) diamond electrodes and reference substrates comprising silver and tin, has been investigated. The abrasion process produced metallic particulates on the electrode surface, and both the mechanical and electrical contact were sensitively dependent on the abrasive force used. Only a small fraction of the material transferred was removed during electrochemical stripping. The silver deposited yields an analytically diagnostic signal in stripping voltammetry; data for tin was found to be extremely dependent on the stripping conditions employed. The initially hydrogenated diamond electrodes were shown to become significantly oxidised when employed in this application.

The decomposition of ultrathin layers of SiO2 on Si(1 1 1) has been studied in real time in a high temperature scanning tunnelling microscope. Deposition of Au onto the SiO2 surface lowers the temperature of decomposition from 1000 to 940 K. Film decomposition takes place initially at step edges. The mechanism is shown to involve nucleation of Au nanoparticles at step edges, “sinking” of the Au particles to the buried SiO2/Si interface and accelerated reaction of substrate Si with SiO2 around Au nuclei. The Au/Si surface left after film decomposition supports a row-like reconstruction with a periodicity six times that of Si(1 1 1).

The surface reactivity of CVD diamond films, which function as UV photocathodes, with thermal and electronically excited O2, as well as atomic oxygen, has been explored. The CVD films show a low, but measurable reactivity with O2, which increases markedly with electronic excitation, to form dilute oxygen adlayers which are stable thermally to 800 K. In contrast, reaction with atomic O produces significantly higher surface concentrations of oxygen, although these adlayers decompose thermally below 500 K, evolving CO2. Greater surface reaction probabilities are observed if the diamond surface is pre-hydrogenated before interaction with oxygen. The consequences of these observations for the stable operation of H-terminated diamond photocathodes are discussed.

X-ray photoelectron spectroscopy has been used to investigate the interaction of xenon difluoride at chemical vapour deposited, polycrystalline diamond surfaces. Dissociative chemisorption, resulting in the formation of adsorbed fluorine up to monolayer coverages, occurs on the clean surface with a sticking probability of approximately 10−4. Prehydrogenation of the diamond, increases the initial reactive sticking probability, but reduces the saturation fluorine coverage observed. Two forms of adsorbed fluorine are clearly detected. The most thermally stable species, which is produced during initial xenon difluoride exposures, is attributed to covalently bonded carbon monofluoride functionalities. A second species, which is more weakly bound, has the characteristics of semi-ionic fluorine, which has been observed previously in the interaction of fluorine with other carbon forms. Thermal desorption studies show that the adsorbed fluorine desorbs over a large temperature range (40–800°C), reflecting the varying thermal stabilities of the differing populated states. Etching of a fluorine-saturated surface with hydrogen atom fluxes shows two main regimes; initial rapid removal of the semi-ionic fluorine species, followed by the very slow abstraction of covalent CF species. The comparative behaviour of the chemically vapour deposited diamond films with diamond single crystal surfaces, with regard to the chemistry observed, is discussed.

Redox processes of the reactive dye, Procion Blue, at polycrystalline boron-doped diamond film electrodes, in buffered aqueous solution are studied as a function of pH, dye concentration and ultrasound treatment. Direct partial oxidation with a four electron transfer, within the solvent window up to 2.5 V vs. SCE in PBS, at pH 2 is possible. However, more extensive degradation of Procion Blue does not occur at potentials below that required for solvent decomposition. Oxidation is most easily achieved in acidic solution and at low dye concentrations, as evidence of fouling of the electrode surface was noted under more alkaline conditions and at higher dye concentrations. The dye is also found to influence redox processes which are directly associated with defect sites on the diamond electrode itself.

•Fabrication of low-cost photocathode by electrochemical method is described.•Boron-doped diamond is presented as catalyst support.•NiO nanoparticles on Cu2O surface enhances photocurrent and electrode stability.•Synergy of metallic interaction between Cu and Ni leads to high efficiency.Herein, we report a novel photocathode for the water splitting reaction. The electrochemical deposition of Cu2O particles on boron doped diamond (BDD) electrodes and the subsequent decoration with NiO nanoparticles by a dip coating method to act as co-catalyst for hydrogen evolution reaction is described. The morphology analysis by scanning electron microscope (SEM) revealed that Cu2O particles are cubic and decorated sporadically with NiO nanoparticles. X-ray photoelectron spectroscopy (XPS) confirmed the electronic interaction at the interface between Cu2O and NiO through a binding energy shift of the main Cu 2p peak. The photoelectrochemical (PEC) performance of NiO-Cu2O/BDD showed a much higher current density (−0.33 mA/cm2) and photoconversion efficiency (0.28%) compared to the unmodified Cu2O/BDD electrode, which are only −0.12 mA/cm2 and 0.06%, respectively. The enhancement in PEC performance is attributable to the synergy of NiO as an electron conduction mediator leading to the enhanced charge separation and transfer to the reaction interface for hydrogen evolution as evidenced by electrochemical impedance spectroscopy (EIS) and charge carrier density calculation. Stability tests showed that the NiO nanoparticles loading content on Cu2O surface is a crucial parameter in this regard.

The permselective properties of stable opal films formed by polystyrene nanospheres on boron-doped diamond (BDD) electrodes were studied for the first time by means of electrochemical voltammetric and impedance techniques. Films formed from spheres with a diameter above 200 nm are highly porous and have little influence on electrochemical properties. In contrast, porous films formed from 50 nm spheres have a selective influence on the electrochemistry observed, providing an enhancement in the redox peak current for neutral (ferrocenemethanol, dopamine) and positively-charged redox probe mediators (Ru(NH3)63+) and suppressing the current due to a negatively-charged redox species Fe(CN)64−. This is because the latter is repelled from the film, whereas the former are selectively partitioned within it. Partition coefficients, film permeability and diffusion coefficients of species within the polystyrene opal layer are determined. It is shown that a Langmuir isotherm analysis for adsorption on the polystyrene sphere surface can describe successfully the incorporation of ferrocenemethanol and Ru(NH3)63+ within the thin film, with Gibb's free energies (ΔG°) of adsorption in the range of −27 to 28 kJ mol−1. Apart from influencing the magnitude of the detected electrochemical response, it is also shown the opal film increases the resistance to electrode fouling by the reaction products formed by the oxidation of dopamine. Electrochemical impedance measurements further illustrate the effects of the polystyrene layer.

We report electrochemical detection of single-catalase collisions at diamond ultramicroelectrodes and show the operative mechanism involves direct enzyme-mediated charge transfer between electrode and solution. Hydrogen peroxide increases the collision frequency, which fluorescence correlation spectroscopy diffusion measurements suggest stems from an increase in the diffusion rate as the underlying cause.

The hot filament chemical vapour deposition of boron-doped diamond was optimised for the fabrication of diamond ultramicroelectrodes. Applications of ultramicroelectrodes require thin, conformal and non-porous diamond coatings, which display electrochemical properties similar to those associated with good quality doped diamond electrodes. The growth conditions to attain these goals are elucidated. The influence of the use of nanodiamond ultrasonic seeding prior to growth, in order to promote nucleation, and varying the negative electrical bias and methane concentration during growth, to control the growth chemistry, are explored. Although Raman spectroscopy shows a deterioration of diamond phase quality with increased negative bias voltage during growth, cyclic voltammetry indicates an improved electrochemical performance due to decreased porosity at reduced grain size under moderate bias voltage. At even higher bias voltage, the electrochemical properties deteriorate due to aggregation of sp2 hybridised carbon at grain boundaries. By combining efficient nucleation methods and appropriate methane concentrations and electrical bias during growth, small grain polycrystalline diamond coatings can be obtained, which show optimal electrochemical properties most suitable for ultramicroelectrode applications.