Proton–hydride tautomerism in hydrogen evolution catalysis

Efficient generation of hydrogen from renewable resources requires development of catalysts that avoid deep wells and high barriers. Information about the energy landscape for H_2 production can be obtained by chemical characterization of catalytic intermediates, but few have been observed to date. We have isolated and characterized a key intermediate in 2e^– + 2H^+ → H_2 catalysis. This intermediate, obtained by treatment of Cp*Rh(bpy) (Cp*, η^5-pentamethylcyclopentadienyl; bpy, κ^2-2,2′-bipyridyl) with acid, is not a hydride species but rather, bears [η^4-Cp*H] as a ligand. Delivery of a second proton to this species leads to evolution of H_2 and reformation of η^5-Cp* bound to rhodium(III). With suitable choices of acids and bases, the Cp*Rh(bpy) complex catalyzes facile and reversible interconversion of H^+ and H_2

1-D Heat Conduction in Porous Layers for Electrochemical Energy Conversion

Polymer electrolyte fuel cells (PEFCs) and electrolyzers show promise in enabling renewable energy source technologies such as solar and wind. Thermal management is an important aspect in the operation of these devices because it can have adverse effects on performance and durability. The porous transport layers (PTLs)/gas diffusion layers (GDLs) are porous thin layers that have many functions in both electrolyzers and fuel cells. One of their functions is to uniformly distribute heat, whereas the function of the porous flow fieldsis to distribute fluids. Knowledge of the thermal conductivity of these components is necessary when optimizing heat transport and modeling thermal distributions in PEFCs and electrolyzers. To this end, the through-plane effective thermal conductivity of a sintered and fiber titanium PTL, carbon based GDL, and nickel chromium flow field mesh is investigated ex-situ for the first time through experimental work for all the materials and computed tomography for the PTLs.Fourier’s law was used to calculate thermal conductivity through a steady-state method. An apparatus was built and designed to measure the heat flux through layers of an individual sample and temperatures at designated points. The effective thermal conductivity of the dry, wet, and tomography calculated sintered Ti PTL is 0.46 ± 0.21 Wm-1K-1, 0.91 ± 0.10 Wm-1K-1, 7.66 Wm-1K-1, respectively. For the fiber Ti PTL, measured values are 0.41 ± 0.07 Wm-1K-1, 0.78 ± 0.46 Wm-1K-1, and 5.22 Wm-1K-1. The effective thermal conductivity of the GDL is 0.32 ± 0.05 Wm-1K-1 and 0.17 ± 0.03 Wm-1K-1 for the NiCr porous flow field mesh. It is shown that the thermal conductivity of the PTLs increases by a larger amount than expected when water is present. The studies presented here illustrate the importance of continued work in thermal characterization of the porous materials used in electrochemical energy conversion and storage