We discuss novel theoretical design of highly efficient energy materials including electrocatalysts for hydrogen evolution reaction (HER), oxygen eveolution reaction (OER), water splitting, oxygene reduction reaction (ORR), and fuel cells, where single atoms (SAs) and nanoparticles (NPs) of transition metals are embedded in graphitic carbon sheets and nanotubes. These catalysts requires very low overpotential to achieve a certain current density as well as impressive stability. To elucidate the origins of catalytic activity and durability, the reliable calculations are essential. However, the accuracy of such calculations are not yet so reliable. These issues will be discussed. Then, after choosing optimal density functional theory (DFT) calculation methods, we design diverse highly efficient electrocatalysts and then compared with experiments. We also discuss a hidden role of A-site organic cations in hybrid halide perovskite solar cells which are uncovered with Fröhlich polaron picture based on first principles and many body theory. In Fröhlich polaron picture, A-site organic cations reduce a coupling between photo-excited carriers and lattice, thus enhancing the lifetime of carriers. This provides a design principle of A-site organic cation towards high performance perovskite solar cell material design. PbI2/AI-terminated lead-iodide-perovskite (APbI3; A=Cs+/ methylammonium(MA)) interfaced with the charge transport medium of graphene or TiO2 is predicted to exhibit the sizable/robust Rashba-Dresselhaus (RD) effect by using DFT and ab initio molecular dynamics (AIMD) simulations at cubic-phase temperature. At the PbI2-terminated graphene/CsPbI3(001) interface, ferroelectric distortion towards graphene facilitates an inversion breaking field. At the MAI-terminated TiO2/MAPbI3(001) interface, the enrooted alignment of MA+ towards TiO2 by short-strong hydrogen-bonding and the concomitant PbI3 distortion preserve the RD interactions even above 330K. The robust RD effect at the interface even at high temperatures, unlike in bulk, changes the direct-type band to the indirect-type to suppress recombination of electron and hole, thereby letting these accumulated carriers overcome the potential barrier between perovskite and charge transfer materials, which promotes the solar-cell efficiency.

Theoretical design of energy materials: Electrocatalysts and perovskite solar cells

2019 Fall National Meeting

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