The development of alkaline anion exchange membranes (AEM) has allowed for a myriad of new liquid fuels to be used in fuel cell applications that cannot be effectively oxidized under acidic conditions using proton exchange membrane fuel cells (PEMFCs). Moreover, many of these fuels are readily electrooxidized by non-platinum group metal catalysts under basic conditions. Interested in the direct formate fuel cell (DFFC), we have explored the activity of palladium supported on reduced graphene oxide (Pd/rGO) toward the formate oxidation reaction in the alkaline medium. The reduction of GO to rGO and synthesis of Pd nanoparticles were confirmed using X-ray diffraction, Raman, and X-ray photoelectron spectroscopies. The surface morphology was evaluated by scanning electron microscopy and transmission electron microscopy. Half-cell studies demonstrated superior electrocatalytic activity and stability toward formate electrooxidation for Pd/rGO than commercial Pd/C catalysts. A low metal loading AEM DFFC, fabricated with a Pd/rGO anode catalyst, displayed a 15% increase in maximum power density at 60 °C compared to the commercial Pd/C catalyst.

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The challenging environment of high temperature and high pressure on the Venus surface limit the battery options for Venus landers and surface probes. High temperature batteries employing Li alloy anodes, molten salt electrolytes and FeS cathodes were demonstrated to be resilient and operational for several days. For further improvements in performance, i.e., both specific energy and operational life, new high-capacity cathode materials are needed. Transition metal phosphorus trisulfides (TMPS3) are promising with considerably higher (2X) specific capacity, specific energy and energy density, by virtue of their ability to react with more than two lithium ions. This papers describes the assessment of these cathodes for high temperature batteries to power future Venus landers and probes. Manganese, iron, cobalt and nickel phosphorus trisulfides were synthesized and characterized by Scanning Electron Microscopy (SEM)/Energy Dispersive X-ray Spectroscopy (EDAX) and X-ray Diffraction (XRD) and tested in our high-temperature laboratory cells at 475 °C using cyclic voltammetry (CV) and galvanostatic discharges at different rates. Mn, Fe and Ni phosphorus trisulfides showed reversible behavior in cyclic voltammetric measurements. In the discharge tests, NiPS3 displayed the highest capacity out of the three metal phosphorous trisulfides tested at both C/20 and C/720 rates, with higher voltages and slightly higher capacity than FeS, followed by FePS3, while MnPS3 displayed relatively poor performance at C/20. Cathodes extracted from the discharged cells contain the transition metal (Fe, Ni or Mn) and Li2S by XRD, as expected from the reaction scheme.

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