Oliver J. Murphy

Direct electrochemical oxidation of organics for wastewater treatment

Abstract A single cell electrochemical reactor that utilizes a proton exchange membrane (PEM) as a solid electrolyte was investigated for the treatment of waters with low or negligible electrolyte content. The electrochemical reactor concept, test system design, the role of the proton exchange membrane and the principle of organic impurity oxidation at PEM/electrocatalyst interfacial reaction zones are outlined. Test data and kinetic analysis are presented. The feasibility and application for water reclamation processes in controlled ecological environments (e.g. lunar/Mars habitats) are discussed. The approach has potential as a terrestrial water pollution control method.

A one-unit photovoltaic electrolysis system based on a triple stack of amorphous silicon (pin) cells

Abstract An arrangement is suggested in one-unit photovoltaic electrolysis whereby the land area needed can be halved.

Products found in the anodic oxidation of coal

Abstract Lignite has been used to depolarize the anodic reaction in aqueous electrolysis. The nature and concentration of the anodic products has been investigated. Iron was removed from coal by washing. Slurries were made of lignite, grass and wastes. Electrolytes were H2SO4, H3PO4 and NaOH. Temperatures were 80–130°C. Sep-pak cartridges were used for separating coal-derived organic liquids from the aqueous electrolyte phase. (Analysis was performed at the University of Texas, Austin, Texas; Radian Corporation, Austin, Texas, and Battelle, Northwest Laboratory, Richland, Washington.) A liquid-liquid extraction procedure was also used (Battelle, Northwest Laboratory). GC/MS was used to identify products (either by use of computer pattern recognition limits or by comparison with mass spectra of standard compounds). Dissolution of washed lignite to ca 0.1 wt% occurs in 5 M H2SO4 at 100°C. Cyclic voltammograms (lignite) show peaks at 0.9 and 1.15 V (NHE). The limiting current densities of systems of lignite in contact with the electrode were three times greater than those obtained on a filtrate of the slurry. About 90% of the current in the washed lignite was from the oxidation of organic compounds. Addition of Ce4+/Ce3+ caused a substantial increase in current density. PbO2 as electrode gave qualitatively similar results to those on Pt, but the currents were 100 times less. Biomass and household wastes gave similar results to those for lignite, but the current densities at similar slurry concentrations were ten times less than with coal. The Sep-pak cartridges produced hydrocarbons themselves in solution, and these were monitored and taken into account, so that only compounds found to occur as a result of electrolysis are reported. These were largely C8–C18 hydrocarbons (ca 10−3 M each, after three hours of electrolysis). Such results were obtained at the University of Texas, Austin, and at the Radian Corporation, Austin, and were confirmed by matching of patterns found against those with known compounds. In corresponding GC/MS investigations (Battelle, Northwest Laboratory), using liquid-liquid extractions, differing results were obtained—a lactone and some hydrocarbons were found. Reasons are given for accepting the results from the University of Texas and Radian Corporation. A comparison of the charge passed with the concentration of organics obtained is consistent with the results from the University of Texas and Radian Corporation. Monolayer dissolution from porous lignite accounts for the material present. Peaks are due to organic reactions. A Kolbe-type process as the basis of the hydrocarbons is discussed. The efficacy of contact between coal and the electrode is due to abrasion. The observed limiting currents are consistent with the organics present (University of Texas and Radian Corporation). The results suggest that increase of temperature to 150°C with enhanced stirring should give ca 750 mA cm−2 limiting current density. Heavy oil may then be extractable from the anolyte; if this is attainable, the credits taken would make pure electrolytic hydrogen comparable in cost with natural gas.

Photovoltaic electrolysis: hydrogen and electricity from water and light

Abstract Two photovoltaic couples, consisting of n on p and p on n gallium arsenide, respectively, have been converted into a water splitting device. Light is allowed to fall on the p part of one couple, which is in contact with air, and on the n side platinum is plated, which contacts the solution. On the other couple, the n side is in contact with air, while on the p side ruthenium dioxide is plated, which is in contact with the solution. Such a device gives a performance (8% conversion efficiency of solar light to hydrogen) better than that of known photoelectrolysis devices operating without battery assistance. Comparison with a coupled photovoltaic-distant water electrolyzer shows, under certain circumstances, some advantages for the present device.

The oxidation state and coordination environment of chromium in a sealed anodic aluminum oxide film by x-ray absorption spectroscopy

Abstract Chromium K -edge XANES (X-ray Absorption Near Edge Structure) and EXAFS (Extended X-ray Absorption Fine Structure) data were obtained for a thick, porous aluminum oxide film sealed in dichromate solution. Analysis of the XANES data indicates that the film contains Cr 6+ ions in tetrahedral ligand fields of oxygen atoms, consistent with the presence of a chromate-like anion, [CrO 4 ] 2+ . Analysis of the EXAFS data provides an average Cr-O interatomic distance and Debye-Waller factor of 0.165 and 0.0053 nm, respectively, which are in good agreement with those for the chromate anion in Na 2 CrO 4 -4H 2 O. These results, in combination with the previous ones of Hawkins et al. [Corros. Sci. 27 , 391 (1987)], suggest that the reduction of adsorbed Cr 6+ to Cr 3+ is dependent upon the thickness of the alumina film.

An amorphous silicon-based one-unit photovoltaic electrolyzer

A one-unit photovoltaic electrolyzer, fabricated from double-stacked amorphous silicon cells (pin-pin), is described. A solar energy conversion efficiency to hydrogen of 2.6% has been achieved, which, with recent technological developments, can be raised to 6%. A one-unit array (with storage) capable of supplying solar hydrogen to power tractors on the average farm would give rise to a cost of ca. 6.2¢/kWh, using the expected 1990 value of

The Electrochemical Splitting of Water

1 per peak W for amorphous silicon photovoltaics. The cost of the hydrogen derived from the system is ca. two to three times that of conventional gasoline per gallon equivalent.

Photoelectrochemical behavior and surface characterization of some lanthanum-based perovskite oxide electrodes

The electrochemical production of hydrogen as an energy medium is becoming economically feasible. The technology is established; it is clean and requires no extra separation or purification of products; it generates suitable pressures for storage and can be used in a modular mode.

The photoelectrochemical production of chlorine from sea water

Abstract The photoelectrochemical response of a number of perovskite oxide anodes, prepared by heating titanium or tungsten-coated discs with a paste of La 2 O 3 with each of the oxides, Cr 2 O 3 , RuO 2 , PtO 2 , Au 2 O 3 and Co 2 O 3 , have been studies. The titanium-supported photoanodes exhibited a higher photoactivity, for oxygen evolution, compared to the tungsten-supported electrodes. From the photoelectrochemical spectra of La 2 O 3 Cr 2 O 3 /Ti and La 2 O 3 RuO 2 /Ti, the band gaps were calculated to be 2.0 and 2.8 eV, respectively. A mixed spectral response was observed for the lanthanides of gold and cobalt. The absolute efficiency for the biased cells containing La 2 O 3 Cr 2 O 3 /Ti and La 2 O 3 RuO 2 /Ti as photoanodes was as high as 5% for the solar spectrum. High resolution X-ray photoelectron spectra for the atomic constituents of the La 2 O 3 Cr 2 O 3 /Ti photoanode, at various depths from the surface, were obtained. The most intense chromium peak was identified as arising from lanthanum chromite (LaCrO 3 ), while titanium in the +4 oxidation state was detected on the surface at low intensity. It was observed that the major product of the reaction between La 2 O 3 and Cr 2 O 3 was LaCrO 3 , the minor product being La 2 (CrO 4 ) 3 . The photoresponse of the La 2 O 3 Cr 2 O 3 /Ti electrode material was attributed to LaCrO 3 and/or La 2 (CrO 4 ) 3 , which have known d-d band splitting in the range 1.6–2.2 eV.

Post-Treatment of Reclaimed Waste Water Based on an Electrochemical Advanced Oxidation Process

Abstract An examination has been made of the evolution of Cl2 from saline solution upon photo-irradiation of certain photo anodes. Photo illumination by means of a Xe lamp was used, and the light chopped to find the photo response. Electrodes were prepared by heating T2O3 or TO2 with R2O3 in argon (T=transition metal, R=rare earth; T=Cr, Ru, Pt; R=La). Electrodes were mounted in Teflon and examined microscopically. The i-V curves were quasi-exponential; iλ-λ relations were parabolic, with two peaks in certain systems. LaRuO3 on Ti evolved Cl2, but LaCrO3 on Ti evolved O2 from saline solution. Current efficiencies were 0.1–1%. A GaAs self-generating cell gave 0.01–0.1% quantum efficiency. When an anion exchange membrane was present, changes indicated the formation of NaOH in the anode compartment. The onset potential is 1.3 V cathodic to the potential for oxygen evolution. On the cathodic side, it is 0.4 V anodic to the potential for hydrogen evolution. The photoelectrochemical spectrum shows two maxima for LaCrO3 on Ti. Quantu, efficiency increases with increase of anodic potential. The phenomenology of the onset potential and onset frequency are qualitatively rationalized. A potential sea-borne caustic, chlorine, ammonia, hydrogen and fresh water, solar-aided plant is described.