This study provides an analysis of the technological barriers for all-electric vehicles, either based on batteries (BEVs) or on H 2 -powered proton exchange membrane (PEM) fuel cells (FCEVs). After an initial comparison of the two technologies, we examine the likely limits for lithium ion batteries for BEV applications, and compare the projected cell-and system-level energy densities with those which could be expected from lithium-air and lithium-sulfur batteries. Subsequently, we will review the current development status of H 2 PEM fuel cells, with particular attention to their viability with regards to the required amount of platinum and the resulting cost and availability constraints. It is widely accepted that global warming is caused by CO 2 emissions and that they must be substantially reduced in order to prevent climate change. Since ≈23% of the world-wide CO 2 emissions are due to transportation, ≈75% of which are contributed by the road sector (numbers from 2012 1 ), a reduction of CO 2 emissions from vehicles is imperative to combat global warming. Towards this goal, many countries have passed legislature to lower passenger vehicle emissions over the long term like, e.g., the European Union mandate for 95 g CO2 /km fleet average emissions by 2020.2 The analysis by Eberle et al. 3 in Figure 1 suggests that this rather ambitious goal can only be met by means of extended range electric vehicles or all-electric vehicles in combination with the integration of renewable energy (e.g., wind and solar). Without increased integration of renewable energy sources and basing the calculations on the current European electricity generation mix, the only vehicle concept which could meet the 95 g CO2 /km target are pure battery electric vehicles (BEV100 in Fig. 1). However, for electricity produced entirely by renewable energy sources, the 95 g CO2 /km target could also be met by extended range electric vehicles with 40 miles all-electric range (E-REV40 in Fig. 1), if 50% of driving is powered by the battery (i.e., the average driving range would have to be below 80 miles), or by fuel cell electric vehicles (FECVs), with hydrogen produced by water electrolysis. While these propulsion concepts look promising, their contribution to CO 2 emission savings in the transportation sector would only be meaningful if their market penetration were substantial. In the absence of government regulations, the latter largely hinges on consumer acceptance, which in turn strongly depends on cost. In addition, in the case of BEVs, recent studies clearly showed that BEV driving range (closely followed by cost) are the predominant variables determining consumer acceptance. 4 In the following we will thus focus on the two vehicle types, which would be capable to meet and exceed the CO 2 emission targets of 95 g CO2 /km on the long-term, viz., pure BEVs and hydrogen powered FCEVs. For both vehicle types, but particularly for the latter, meaningful CO 2 emission reductions require the predominant use of renewable energy, which in turn necess...

A novel high-throughput technique has been developed for the investigation of the influence of supported metal particle size and the support on electrocatalytic activity. Arrays with a gradation of catalyst particle sizes are fabricated in a physical vapor deposition system that also allows selection of the support material. Simultaneous electrochemical measurements at all electrodes in the array, together with determination of the actual particle size distribution on each of the electrodes by transmission electron microscopy (TEM), then allows rapid determination of the activity as a function of catalyst center size. The procedure is illustrated using data for the reduction of oxygen on gold nanoparticles supported on both substoichiometric titanium dioxide (TiO(x)()) and carbon and the conclusions are verified using voltammetry at rotating disk electrodes. Gold centers with diameters in the range 1.4-6.3 nm were investigated and it is demonstrated that, with both supports, the catalytic activity for oxygen reduction decays rapidly for particle sizes below 3.0 nm. This may be observed as a decrease in current at constant potential or an increase in the overpotential for oxygen reduction.

The electrooxidation of carbon monoxide on titania- and carbon-supported gold nanoparticles of mean diameters <6.5 nm was studied in 0.5 M HClO4. The samples were prepared by physical vapor deposition, and the activity of the supported particles compared with the reaction at bulk, polycrystalline gold. Carbon-supported gold exhibited activity for CO oxidation only at potentials similar to that observed for bulk gold. Decreasing the particle size below ∼2.5 nm resulted in a sharp decay in catalytic activity. Titania-supported gold exhibited catalytic activity at overpotentials significantly below those of bulk gold, and the activity was strongly particle-size-dependent. A maximum in activity was observed at ∼3.0 nm, and a sharp reduction in activity is observed below ∼2.5 nm. The results highlight two important effects. Titania is responsible for a strong substrate-induced activity for CO electrooxidation on gold particles. In addition to the induced activity at low overpotentials, this titania-supported gold is also shown to exhibit activity at high potentials where normally the oxidation of the gold poisons the reaction. The second observation is that the oxidation is inhibited on particles below 2.5 nm in size, irrespective of the support.

A high-throughput method for physical vapor deposition has been applied to the synthesis of libraries of supported gold particles on amorphous substoichiometric TiO x and carbon supports. The TiO x substrate stoichiometry can be varied or kept constant across a supporting sample, and subsequent deposition of particle sizes on supports are controlled through the nucleation and growth process. TEM measurements indicate nucleation and growth of Au particles takes place, with the smallest particles initially observed at 1.4 nm with a maximum density of 5.5 × 1012 cm-2 on titania, and 2.6 nm with concomitantly lower density on carbon. The 1.4-nm particles on titania exhibit a binding energy shift in the Au(4f) core level of 0.3 eV from bulk gold, and the shift is ∼0.1 eV by the time particles grow to a mean size of 2.5 nm. These shifts are associated with final state effects, and the supported gold particles are metallic and appear to be relatively stable in air. When combined with appropriate substrates and screening techniques, this method provides a highly controllable method for the high-throughput synthesis of model supported catalyst.

A range of reduced titania (TiO(x)) supported platinum electrocatalysts have been synthesised using physical vapour deposition on arrays of electrodes. Surfaces with equivalent thicknesses of platinum in the range 0.2-2.5 nm on a uniform layer of TiO(x) have been synthesised on 10 x 10 arrays. The arrays have been used to study the surface redox chemistry of the supported platinum as well as the oxidation of a monolayer of carbon monoxide on the platinum. It is shown that below an equivalent thickness of 0.8 nm, there is a positive shift in the potential for the oxidation of the platinum surface and a negative shift for the reduction of the oxide with decrease in the platinum loading. These shifts show that it is the kinetics of the platinum/platinum oxide couple that change with platinum loading; the couple becomes increasingly irreversible with decreasing loading. The peak potential for the oxidation of the monolayer of carbon monoxide also shifts positive and broadens with decreasing platinum loading; these trends are again particularly marked below an equivalent thickness of 0.8 nm while below 0.4 nm no CO oxidation peak is observed although it could be confirmed that CO is adsorbed on such surfaces. Again, these changes with platinum loading are associated with the irreversibility of the platinum/platinum oxide couple. At low equivalent thicknesses, it is impossible to form the oxidised platinum species within the carbon monoxide monolayer essential to the commencement of oxidation of the CO monolayer.