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We hypothesized that pressure and temperature affect Li metal solid-state battery (LMSB) resistance and susceptibility to Li metal penetration during cycling. To validate this, the kinetics and stability of the Li-solid electrolyte interface was studied using the model polymer electrolyte system: Li/Polyethylene oxide-LiTFSI (PEO-LiTFSI). It was determined that the interface impedance decreased with increasing pressure and was invariant above 400 and 200 kPa at 60 and 80 • C, respectively. In tests to determine susceptibility to Li metal penetration as a function of current density, it was determined that the current density at which Li metal penetrates PEO-LiTFSI, was consistently 0.5 mA/cm 2 for all temperatures tested (60, 80, and 100 • C). To gain a mechanistic understanding of how Li metal penetrates a solid electrolyte at and above the current density for onset of Li metal penetration, an operando optical visual cell was used. A clear correlation between erratic DC polarization behavior and the onset and propagation of Li metal penetration was made. The empirical observations in this study could help better understand the factors that affect the kinetics and stability of the Li-solid electrolyte interface. We believe these findings could help to advance the maturity of LMSB.

However, the durability and cost of such systems still remain a challenge. [2,3] Using the Department of Energy (DOE) cost-breakdown for the 80-kW net stack for light-duty vehicles, the cost of precious metal electrocatalyst remains almost unchanged as production rate increases to 0.5 M PEFC stacks per year. [4] The cost of the electrocatalyst amounts to 31% of stack cost, for 0.5 M systems per year production rate. [4] Platinum (Pt) or Pt-alloys are used as electrocatalyst for the oxygen reduction reaction (ORR) on the cathode side and the hydrogen oxidation reaction on the anode side of PEFCs. Pt or Pt-alloy electrocatalysts are dispersed as nanoparticles onto carbonblack support. DOE has set a target of reducing Pt loading to 0.125 mg cm −2 to achieve the goal of $12.6 kW net −1 for a stack with power density target of 1.8 W cm −2 . Membrane electrode assemblies (MEAs) with lower catalyst loading are less durable, [1] thus, the cost issue cannot be resolved without focusing on the catalyst durability issue of the PEFC stack. Moreover, heavy-duty trucks (HDTs) require stacks with 25 000-30 000 h lifetime, which to date requires ≥0.4 mg cm −2 [70] Pt catalyst loading. Significant progress in The heterogeneity of polymer electrolyte fuel cell catalyst degradation is studied under varied relative humidity and types of feed gas. Accelerated stress tests (ASTs) are performed on four membrane electrode assemblies (MEAs) under wet and dry conditions in an air or nitrogen environment for 30 000 square voltage cycles. The largest electrochemically active area loss is observed for MEA under wet conditions in a nitrogen gas environment AST due to constant upper potential limit of 0.95 V and significant water content. The mean Pt particle size is larger for the ASTs under wet conditions compared to dry conditions, and the Pt particle size under land is generally larger than under the channel. Observations from ASTs in both conditions and gas environments indicate that water content promotes Pt particle size growth. ASTs under wet conditions and an air environment show the largest difference in Pt particle size growth for inlet versus outlet and channel versus land, which can be attributed to larger water content at outlet and under land compared to inlet and under channel. From X-ray fluorescence experiments Pt particle size increase is a local phenomenon as Pt loading remains relatively uniform across the MEA.

Pt catalyst in polymer electrolyte fuel cells degrades heterogeneously as the catalyst particles are exposed to local variations throughout the catalyst layer during operation. State-of-the-art analytical techniques for studying degradation of Pt catalyst do not possess fine spatial resolution to elucidate such non-uniform degradation behavior at a large electrode level. A new methodology is developped to spatially resolve and quantify the heterogeneous Pt catalyst degradation over a large area (several cm 2 ) of aged MEAs based on synchrotron Xray micro-diffraction. PEFC single cells are aged using voltage cycling as an accelerated stress test and the degradation heterogeneity at a micrometer length scale is visualized by mapping Pt catalyst particle size after voltage cycling. We demonstrated in details that the Pt catalyst particle size growth is non-uniform and follows the flow field geometry. The Pt particle size growth is greater in the area under the flow field land, while it is minimal in the area under the flow field channel. Additional non-uniformity is observed with the Pt particle size increasing more rapidly at the gas outlet area of than the Pt particle size at the inlet area.

A method is described for the measurement of lithium ion transference number and thermodynamic factor of a binary electrolyte by the combined use of anion-exchange concentration cell measurements and concentration cell measurements. The measurements were carried out using cells consisting of LiTFSI salt, a poly(ethylene oxide) solvent, a polydiallyldimethylammonium bis(trifluoromethanesulfonyl)imide anion-exchange layer, and lithium foil electrodes. The transference number and thermodynamic factor were fit using expansions suggested by electrolyte theory. The thermodynamic factor was measured to lie within the range 0.3 to 6 at 80°C. The lithium ion transference number was measured to be 0.18 at infinite dilution and decreased with increasing concentration. Under ideal operation, the anion-exchange concentration cell directly measures the difference in the chemical potential of salt at two different concentrations. The accuracy of the approximation of ideal operation was estimated, showing that the method is more accurate as the salt has low partitioning into the anion-exchange layer and as the salt diffusivity in the anion-exchange layer is lower than in the solvent.