Alloy Oxide Electrocatalysts for Regenerative Hydrogen-Halogen Fuel Cell
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Alloy Oxide Electrocatalysts for Regenerative Hydrogen-Halogen Fuel Cell Sujit K Mondala), Jason Rugolo, Michael J. Aziz1 Harvard School of Engineering and Applied Sciences, Cambridge, MA, 02138, U.S.A. 1 Corresponding author. [email protected]
ABSTRACT Stable, catalytically active, and inexpensive halogen electrodes are essential for the success of the regenerative hydrogen-halogen fuel cell as a competitive means of large-scale electricity storage. We report the synthesis and electrochemical testing of two novel electrode materials — ruthenium-cobalt and ruthenium-manganese alloy oxides. These alloys were fabricated by wet chemical synthesis methods as a coating on a titanium metal substrate and tested for chloride and bromide oxidation and for chlorine and bromine reduction. These alloy oxides exhibit high catalytic potency and good electrical conductivity good stability, while having a significantly reduced precious metal composition compared to commercial chloride oxidation electrodes made of the oxide of a ruthenium-titanium alloy. We tested alloys with Ru content as low as 1% that maintained good electrochemical activity. Stability tests indicate immeasurably small mass loss.
INTRODUCTION There are many means of storing electrical energy, but only a few are feasible for the power levels, costs, and energy storage capacities required to support grid scale intermittent renewable energy production and use. Among these are flow battery systems that involve hydrogenhalogen, vanadium redox, and zinc bromine chemistries. We expect the hydrogen-halogen flow battery or regenerative fuel cell to become a competitor because of the low overpotentials afforded by the halogen electrode, leading to very high roundtrip efficiencies at reasonable current densities; the high energy density; and the inexpensive reactants. The corrosive halogen and hydrohalic acid environment provides a materials challenge, however. Making low cost, high performance, durable electrodes is essential for the success of the technology. Commercial chloride oxidation electrodes are based on DeNora's Dimensionally Stable Anode (DSA), which is an oxide of the RuxTi1-x alloy, with x typically greater than 30% [1]. DSAs have superb electrocatalytic properties for chloride oxidation at highly anodic potentials. The DSA electrode kinetics of the chlorine oxidation reaction have been studied extensively [2-5].
Hydrogen-halogen based regenerative fuel cell electrodes require an inexpensive electrocatalyst for both oxidation and reduction reactions that is a good electron conductor with a surface that is stable below a pH of 0. Hydrogen-halogen based regenerative fuel cells from the 1980s employed comparable electrode materials to DSAs [7]; other carbon-supported and noble metal containing oxide catalysts have also been investigated [8]. The hydrogen electrode is similar to hydrogen-oxygen PEM fuel cells; hence we expect the attainable precious metal loading on the hydrogen electrode to be similar to optimal loadings in hydrogen-oxygen fuel cells [9]. Hyd
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