This paper is about the continuous electrochemical conversion of carbon dioxide to formate in a polymer electrolyte membrane cell using an alkaline ion-exchange membrane sandwiched between two catalyzed electrodes. This type of cell configuration allows carbon dioxide conversion to occur at high efficiencies and is particularly attractive for large-scale implementation. Formate was produced at high efficiency, and hydrogen evolution was suppressed with lead and indium as catalysts. The production of formate was monitored by UV-visible spectroscopy. During short experimental runs, the faradaic efficiency of formate production was as high as 80%. The faradaic efficiency was strongly dependent on the concentrations of carbon dioxide, bicarbonate, and carbonate at the surface of the electrodes. Low concentrations of carbon dioxide in the reactant feed led to the mass transport limitations and hence low faradaic efficiencies. The results show that mass transport limitations can be mitigated and high efficiencies can be realized by conducting the electrolysis in a pulsed mode. An alkaline membrane-based flow cell that ensures abundant availability of carbon dioxide to the electrodes can be a cost-effective and efficient approach for the continuous production of fuels from sunlight, storing of renewable energy, and lowering carbon dioxide levels in the atmosphere.

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Performance of direct methanol fuel cells with sputter-deposited Pt-Ru anodes was investigated. The thin film catalyst layers were characterized using X-ray diffraction, energy dispersive X-ray analysis, Rutherford backscattering spectroscopy, and X-ray photoelectron spectroscopy. Different catalyst loadings and membrane electrode assembly (MEA) fabrication processes were tested. The maximum power density achieved at 90°C was 100 mW/cm 2 , and almost 75 mW/cm 2 was attained with a loading of only 0.03 mg/cm 2 . The results demonstrate that a catalyst utilization of at least 2300 mW/mg can be achieved at current densities ranging from 260 to 380 mA/cm 2 . The application of the sputter-deposition method for MEA fabrication is particularly attractive for commercialization of direct methanol fuel cell technology.

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A combinatorial approach to batch fabricating and evaluating fuel cell catalyst surfaces is described. The well-known binary Pt/Ru alloy and two compositional regimes of a novel quaternary Ni/Zr/Pt/Ru system were examined in detail. Catalyst films no thicker than 10 nm were deposited onto an array of 36 gold electrodes 0.5 cm 2 in area that were microfabricated on a 12.5 ϫ 12.5 cm glass substrate. The catalyst films had identical bulk and surface compositions, a result of the atom-level mixing that occurred during the room-temperature cosputtering method used. A multichannel pseudopotentiostat was implemented for electrochemical screening. Compositions with promising and/or contrasting catalytic activities were also studied using X-ray diffraction, X-ray energy-dispersive spectroscopy, and X-ray photoelectron spectroscopy. A low-Pt-content Ni 31 Zr 13 Pt 33 Ru 23 film was found to exhibit nominally the same activity ͑at 0.45 V vs a normal hydrogen electrode in 1 M H 2 SO 4 , 1 M CH 3 OH͒ as the best PtRu alloys studied. This material had a fundamentally different crystal and electronic structure than that observed in the Pt/Ru films and exhibited a significantly higher degree of Pt site utilization. These results were consistent with the existence of a catalytic reaction pathway different than that reported for Pt/Ru. Methodologies for optimizing anode catalysts for direct methanol fuel cells ͑DMFCs͒ have been under development since the 1980s. 1 A primary goal has been to minimize the cost associated with mass-producing fuel cells by limiting or even eliminating the amount of precious metal necessary for achieving good electrical performance. Typically, DMFC anode assemblies consist of a fibrous carbon paper loaded with 2-8 mg/cm 2 of Pt/Ru black. Efforts to improve the electrocatalytic activity have focused on maximizing the surface-area-to-volume ratio of the catalyst materials, either by creating nanostructured powder materials or by dispersing small catalyst grains on larger carbon particles. [2][3][4] Other results have shown that alternate chemistries may be appealing, and several research groups have reported catalyst alloy materials that contain little or no Pt yet retain some catalytic functionality. In particular, it has been demonstrated that the addition of Ni, Co, V, Fe, Cu, and Mo to Pt/Ru may enhance catalyst performance. 5-7 Others have found that some binary alloys containing Ni and Ti, Nb, Ta, or Zr can function as Pt-free methanol catalysts, though the reported current densities are substantially lower than those typically reported for commercial Pt/Ru powders. 8,9 In many of the studies on novel catalysts, the actual mechanisms driving the reactions of interest are not well described. There are multiple, sometimes contradictory theories used to explain the observed effects. [10][11][12][13] Confounding this issue is the fact that contrasting ͑often unpublished and proprietary͒ synthesis routes are used to create catalyst materials ͑typically in powder form͒, each resulting in significantly di...