New electrodes for oxygen evolution in acidic solution

Abstract

Conventional electrowinning of metals such as zinc and copper from 1-1.5 kmolm -3 H2SO 4 electrolytes involves anodic oxygen evolution at Pb alloy/PbO2 anodes operating at 200-800 A m -2. The oxygen overpotential, estimated to be about 0.6V, constitutes a significant proportion of the cell voltage (typically 2.5 V for Cu and 3.3 V for Zn). The objective of this work was to lower the anode overpotential and so decrease the process specific energy requirements, by devising new anode materials based on: (1) PTFE-bonded PbO2 catalysts, supported on Pb-Ag alloys; (2) modification of the pore structure of porous electrodes to maximize the utilization of the available surface without the use of PTFE bonding. Both methods are shown to produce significant benefits in lowering oxygen overpotentials, though the latter technique has been tested only in alkaline electrolytes, as yet. However, with the former approach, substrate oxidation through the porous catalyst layer has been found to cause catalyst shedding after > 60 h at 1 kA m -2, though careful pre-oxidation of the anode substrate appears to extend the anode life.

Reactive Deposition of Cobalt Electrodes: IV . Alkaline Water Electrolysis

“…This is analogous to the operation of Teflon bonded electrodes (4). However, the absence of inert and non-conducting Teflon particles and the high conductivity account for the superior performance of the reactively deposited Co electrodes as compared to Teflon bonded electrodes (9). The high utilization of inner surface area of the electrodes and the high electrochemical efficiency have been confirmed by the linear relationship of the electrochemical performance of the electrodes as a function of the Co loading.…”

“…For the same electrodes operating at 1 A/cm 2 and 80~ the overpotentials were determined to be 0.264 V for H2 evolution and 0.285 V for O2 evolution, respectively, after being polarized for 15 h. The very low IR losses also show that the electrical conductivity of the reactively deposited porous Co electrodes is very high, as compared to Teflon-bonded electrodes. In the case of Teflon-bonded electrodes, the IR losses are typically in the range of 120 mV at a current density of 1 A/cm 2 with catalyst loading of about 20 mg/cm 2 (9).…”

“…During anodic oxidation of lead electrode in sulfuric acid solution, the behavior of the anodic layer formed has been extensively studied (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). When lead electrode is polarized in sulfuric acid solution in the potential region lying between the equilibrium potentials of Pb/PbSO4 and PbSO4/PbO2 electrodes, a dense crystalline layer is formed and passivates the lead electrode.…”

“…Previous studies (7,8) have shown that cobalt electrodes produced by the reactive deposition technique have very high surface area and are highly porous, characterized by fine pore and coarse pore network structure. Reactively deposited cobalt anodes performed better in the oxygen evolution mode in alkaline solutions than Teflon-bonded and non-Teflon-bonded porous NiCo20, electrodes (9). Basically, the reactive deposition process involves the deposition of porous metal in the presence of bubbling oxygen and chloride ions in the solution (7,8).…”

A Mass Transfer Study with Electrolytic Gas Production

“…Three main areas have been investigated such as: the bubble formation (Chirkov & Psenichnikov, 1986), the mass transfer and hydrodynamic instabilities at gas-evolving surfaces (Kreysa & Kuhn, 1985), and the behavior of gas in porous electrodes in fuel cells (White & Twardoch, 1988). Many works were developed up to the present about gas-evolving electrodes (St-Pierre & Wragg, 1993a, 1993bVogt, 1979Vogt, , 1984aVogt, , 1984bVogt, , 1984cVogt, , 1989aVogt, , 1989bVogt, , 1992Vogt, , 1994Vogt, , 1997Czarnetzki & Janssen, 1989;Boissonneau & Byrne, 2000;Ellis et al, 1992;Janssen et al 1984;Lastochkin & Favelukis, 1998;Wongsuchoto et al, 2002;Buwa & Ranade, 2002;Gabrielli et al, 2002;Correia & Machado, 1998;Lasia, 1998;Iwasaki et al, 1998;Fahidy & Abdo, 1982;Lasia, 1998Lasia, , 1997Barber et al, 1998;Eigeldinger & Vogt, 2000;Solheim et al, 1989;Elsner & Coeuret, 1985;Dykstra et al, 1989;Khun & Kreysa, 1989;Lubetkin, 1989;Martin & Wragg, 1989;Lantelme & Alexopoulos, 1989;Gijsbers & Janssen, 1989;Chen, 2001;…”