David Peterson

U.S. DOE Progress Towards Developing Low-Cost, High Performance, Durable Polymer Electrolyte Membranes for Fuel Cell Applications.

Low cost, durable, and selective membranes with high ionic conductivity are a priority need for wide-spread adoption of polymer electrolyte membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs). Electrolyte membranes are a major cost component of PEMFC stacks at low production volumes. PEMFC membranes also impose limitations on fuel cell system operating conditions that add system complexity and cost. Reactant gas and fuel permeation through the membrane leads to decreased fuel cell performance, loss of efficiency, and reduced durability in both PEMFCs and DMFCs. To address these challenges, the U.S. Department of Energy (DOE) Fuel Cell Technologies Program, in the Office of Energy Efficiency and Renewable Energy, supports research and development aimed at improving ion exchange membranes for fuel cells. For PEMFCs, efforts are primarily focused on developing materials for higher temperature operation (up to 120 °C) in automotive applications. For DMFCs, efforts are focused on developing membranes with reduced methanol permeability. In this paper, the recently revised DOE membrane targets, strategies, and highlights of DOE-funded projects to develop new, inexpensive membranes that have good performance in hot and dry conditions (PEMFC) and that reduce methanol crossover (DMFC) will be discussed.

Conduction electron density of states and proton spin-lattice relaxation in the dihydrides of scandium, yttrium, lanthanum and lutetium☆

Abstract We report determinations of the proton Korringa product T1eT in the dihydride phases of scandium, yttrium, lanthanum and lutetium based on samples prepared from the highest purity metals available in the Ames Laboratory and in addition in some cases utilizing the technique of partial deuteration to suppress further the paramagnetic impurity contribution to the spin-lattice relaxation rate. We conclude that the quantity (T 1e T) − 1 2 , which is essentially proportional to the electronic density of states N(EF), has the value 0.055 ± 0.002 s − 1 2 K − 1 2 at the dihydride composition in all systems. The dependence of ( T 1e T) − 1 2 on hydrogen concentration within the dihydride phase appears to be weak; however, in LaHx (T1eT)− 1 2 decreases substantially for x ⪢ 2 indicating a decrease in N(Ef) in this hydrogen concentration range. The implications of these results for relative s and d band contributions and hyperfine fields are discussed in the light of recent low temperature heat capacity measurements.

Dynamical evidence of hydrogen sublattice melting in metal-hydrogen systems

Abstract Measurements of the temperature dependence of the proton and deuteron spin-lattice relaxation time T1 in cubic fluorite (CaF2) structure dihydrides and dideuterides (MH2 and MD2) show a second high temperature turndown in T1 in addition to the usual minimum associated with the independent hopping motion of H(D) among tetrahedral (T) interstitial sites at lower temperatures. The close analogy to the motion of anions in fluorite structure superionics suggests that the high temperature minimum indicates the onset of strongly correlated hydrogen motion, possibly accompanied by the occurrence of long-lived hydrogen clusters.

An interpretation of Q∗ in thermotransport

Abstract The heat Q ∗ of transport for the thermotransport of interstitial atoms is resolved into two contributions, one being the activation energy for diffusion and the other arising from an induced biasing of the solute atom jumping by a temperature gradient. The approximation is made that the activation energy for diffusion is negligibly temperature dependent but is the dominant energy barrier to the jumping of solute atoms. Comparison of this interpretation with experimental data indicates that rarely, if ever, is the intrinsic mechanism for thermal transport the sole operating mechanism. The data imply that any single mechanism that can explain the results must be rather complex or, alternatively, that simultaneous operation of two or more mechanisms must be invoked.

Paramagnetic impurity effects in nuclear magnetic resonance determinations of hydrogen diffusion and electronic structure in metal hydrides: Cerium in YH2☆

Abstract We report the results of a preliminary survey of the effects on the proton spin-lattice relaxation time T1 resulting from the presence of controlled low levels of the Kramers ions cerium, neodymium, gadolinium, dysprosium and erbium in YH2. The Ce3+ results in particular are presented in some detail because the cerium ion behaves very differently from the others, reflecting the fact that it is an extremely “fast relaxing” ion. From the measured proton T1 we conclude that the Ce3+ ion spin-lattice relaxation time τi is 1.65 × 10−12s at 77 K.

Heat capacity of well-characterized thorium metal from 298 to 700 K

Abstract The heat capacity of thorium metal has been determined by high temperature adiabatic calorimetry from 302 to 700 K on a relatively pure and well-characterized sample of the metal. The heat capacity of thorium metal from 298 to 700 K is given by Cp(Th,c) (J K−1 mol−1) = 24.905 + 4.049 × 10−3 T + 5.591 × 10−6 T2 where T is in kelvin.

Thermotransport of hydrogen in niobium and tantalum as a function of concentration

Abstract Thermotransport of hydrogen in niobium and tantalum has been measured up to a hydrogen to metal atomic ratio of 0.3. The heat of transport based on the activity ratio decreased as the hydrogen concentration increased in both niobium and tantalum. The heat of transport based on the hydrogen concentration ratio decreased in tantalum but increased in niobium as the hydrogen concentration increased.