Robert John Potter

Surface redox catalysis for O2 reduction on quinone-modified glassy carbon electrodes

Abstract The electrochemical reduction of oxygen on bare glassy carbon (GC) and on electrodes grafted with anthraquinone has been studied using the rotating ring-disk electrode (RRDE) technique. The electrode surface was grafted by the electrochemical reduction of the corresponding diazonium salt. The functionalised electrode showed quasi-reversible redox behaviour in oxygen-free 0.1 M KOH and the cyclic voltammetric response of the surface bound anthraquinone was stable on potential cycling. The covalently attached anthraquinone acts as an electrocatalyst for oxygen reduction and a well defined diffusion limited current plateau was observed in the potential range from −0.75 to −1.25 V (SCE) in 0.1 M KOH. The RRDE results show that oxygen reduction on both electrode surfaces studied stops at the hydrogen peroxide stage. The modified carbon electrodes are potential candidates for the electrochemical production of hydrogen peroxide.

Electrocatalysts for fuel cells

Abstract A brief description of the six main types of fuel cell which are currently under research and development is given. The discussion focuses on recent developments in the polymer electrolyte-based proton exchange membrane fuel cell with description of the limitations imposed by current electrocatalysts and the benefits offered by the development of improved materials.

Flexible dye sensitised nanocrystalline semiconductor solar cells

We report here flexible solid-state solar cells based upon dye-sensitised nanocrystalline Al2O3 coated TiO2 films and an I2/NaI doped solid-state polymer electrolyte. Such devices show remarkably high solar-light to electrical energy conversion efficiencies of approximately 5.3% under 10 mW cm-2 AM1.5 illumination.

A supramolecular approach to lithium ion solvation at nanostructured dye sensitised inorganic/organic heterojunctionsElectronic Supplementary Information (ESI) available: experimental details and absorption spectra. See http://www.rsc.org/suppdata/cc/b3/b306604e/

A novel arylamine based hole transporting material (HTM) with tetraethylene glycol (TEG) side groups is reported. Lithium ions solubilised by the TEG groups are employed to modulate interfacial electron transfer reactions at a dye sensitised TiO2/HTM interface.

A study of the electro-oxidation of methanol on platinum in 1 M Na2SO4 by electrochemical and in-situ FTIR techniques

Abstract The electrochemical oxidation of methanol in unbuffered 1 M Na 2 SO 4 has been studied in order to shed light on the oxidation mechanism. Results from RDE and RRDE measurements suggest that surface poisoning by adsorbed carbonyl species plays an important role, as in acidic solutions, and in situ FTIR studies reveal a rich surface chemistry involving a variety of carbonyl intermediates. The electrochemistry in 1 M Na 2 SO 4 is complicated by pH swings during both oxidation and reduction cycles, and the release of protons can be detected both at the platinum ring and by in situ FTIR. Both stationary electrode and FTIR studies indicate the presence of a substantial cathodic current on sweeping the electrode back from positive potentials where CO 2 formation has taken place. This cathodic process disappears if the electrode is rotated. If methanol is not present, no analogous process takes place, and FTIR data suggest that it may be due to incorporation of surface-bound CO 2 onto a poisoned surface with concomitant reorganisation of adsorbed CO.

In-situ potential modulation difference diffraction studies of platinum in sulphuric acid using synchrotron X-ray radiation

Abstract In-situ potential-modulated X-ray diffraction (XRD) studies of platinized platinum electrodes in 1 M sulphuric acid were undertaken using synchrotron X-ray radiation. During these studies, the potential of the platinized electrodes was repeatedly stepped between values corresponding to the ‘double-layer’ region and oxide formation and potentials within the hydrogen adsorption region. Subtle differences between these sets of XRD patterns led to the conclusion that there was a slight shift in the position of each of the XRD peaks when the electrode potential was changed. These data are consistent with an increase in d -spacing at potentials in the oxide region and a decrease at potentials corresponding to the weakly adsorbed hydrogen region.

An investigation of oxide films on platinum in sulphuric acid solution by electrochemical and photoelectrochemical techniques

Abstract The measurement of photocurrents at polycrystalline platinum electrodes oxidized to different extents in 0.5 mol dm −3 sulphuric acid solution is reported. Small anodic photocurrents were detected in the potential region where the thin α-oxide film begins to grow on platinum. The photocurrent conversion efficiency Φ reached values of the order of 10 −5 at 5.0 eV. Φ was found to depend exponentially on photon energy for an oxide film grown at 1.6 V /RHE, and plots of log 10 Φ vs. hv were linear over the range 2.2–5 eV with slopes close to 1 eV per decade. The photoelectrochemical behaviour of thicker oxide films (α and β) formed by galvanostatic oxidation of platinum in the oxygen evolution region was also examined, and cathodic photocurrents with much higher conversion efficiencies were observed. The photocurrent measured during potentiodynamic experiments on the thicker oxide films has been related to the reduction of the underlying α-oxide phase and of the outer β-oxide phase. The results indicate that both oxide phases are photoactive.

DEMS-monitoring liquid | gas interfacial ammonia oxidation at carbon nanofibre membranes

Electrochemical ammonia oxidation is of interest in waste treatment as well as in electrochemical sensing applications and demonstrated here at a carbon nanofibre (“bucky-paper”) electrode. The electrode is placed at the aqueous electrolyte | gas interface, and current (cyclic voltammetry) as well as ambient differential electrochemical mass spectrometry (DEMS, cyclic voltbarometry) data are recorded as a function of solution composition and pH. The oxidation of oxalate to CO2 is employed as a test and calibration system. Anodic polarization of the carbon nanofibre membrane in inert aqueous electrolyte is shown to result in direct sustained anodic CO2 evolution. In alkaline aqueous media (starting at pH 9) significant levels of nitrogen from ammonia are produced in competition to CO2 formation from carbon nanofibres without the need for additional catalysts. However, for applications with low level ammonia, catalysts will be required to minimize current losses, carbon nanofibre corrosion, and side product formation.

Investigating the feasibility of symmetric guanidinium based plumbate perovskites in prototype solar cell devices

In this work we have studied the feasibility of highly symmetric guanidinium (GA; CH6N3 +) cation in perovskite based solar cells. It is an alternative to the methyl ammonium (MA; CH3NH3 +) or formamidinium (FA; CH(NH2)2+) ions commonly utilized in the perovskite solar cells, may bring additional advantages due to its triad rotational symmetry and zero dipole moment (μ). We noticed that due to steric factors, GA preferably forms two-dimensional (2D) layer, where GA2PbI4 is favored monoclinic structure (E g = 2.5 eV) and the obtained device efficiency is η = 0.45%. This study provides a guideline for designing guanidinium based perovskite absorbers for solar cell devices. In addition, through further compositional engineering with mixed organic cations using GA may enhance the device performance.

Slow charge recombination at a dye-sensitized nanocrystalline TiO2/organic semiconductor heterojunction employing Al2O3 coatings

Control of charge interfacial charge transfer is central to the design of photovoltaic devices. We report herein the application of insulating metal oxide blocking layers to control the charge recombination kinetics at a solid-state dye sensitised nanocrystalline inorganic/organic semiconductor interface. We show that the conformal growth of a ~1 nm thick overlayer of Al2O3 on a preformed nanocrystalline TiO2 film results in a ~3-fold retardation in the rate of charge recombination at such an interface. This observation shows a good correlation with the current/voltage characteristics of dye sensitized nanocrystalline solar cells fabricated from such films, with the Al2O3 coating resulting in a 40% improvement in overall device efficiency