Computational Studies of Energy-Related Materials

Computational modeling plays an increasingly important role in the materials studies. Here we present our computational studies on the materials related to hydrogen and solar radiation, two promising alternative and clean energy solutions. Hydrogen evolution from water can be easily achieved by electrolysis at large overpotentials that can be lowered with expensive Pt-based catalysts. Replacement of Pt with cost-effective and earth-abundant electrocatalysts would be significantly beneficial for large-scale hydrogen generation. The chemically exfoliated WS2 nanosheets can exhibit enhanced electrocatalytic activity. We find that instead of previously recognized active edges in MoS2 of 2H (trigonal prismatic) phase, the surface of as-exfoliated 1T (octahedral) WS2 is taking part in the catalytic reaction and tensile strain is responsible for the experimentally observed low overpotentials. For the photovoltaic materials, we discuss the role of grain boundaries which are ubiquitous in thin-film Cu2ZnSnSe4 absorber materials with earth-abundant constituent elements. The grain boundaries create localized defect states that promote the recombination of photon-excited electron and hole carriers. Therefore, it is essential to effectively remove these defect states in order to improve the conversion efficiency of Cu2ZnSnSe4 solar cells.