Photoelectrochemical Solar Energy Conversion and Hydrogen Evolution Catalysis Using Earth-Abundant Iron Pyrite and Cobalt Pyrite Nanostructures

The scale of the energy challenges demands earth-abundant and inexpensive solar absorber materials and catalysts. Iron pyrite (FeS₂) is an earth-abundant semiconductor that has generated renewed interest due to its promising properties for solar energy conversion (band gap of 0.95 eV, high absorption coefficient, and high carrier mobility). However, the solar conversion efficiency achieved for even single crystal pyrite has remained < 3%, limited by a low open circuit voltage (<200mV).  To understand the fundamental bulk and surface defects intrinsic to pyrite semiconductor, we performed systematic photoelectrochemical and surface property studies on pyrite single crystals and electrical transport (temperature dependent Hall effect and field-effect) studies using single crystal pyrite nanorods and nanoplates as study platforms. The combined electrochemical impedance spectroscopy, surface property and transport studies suggest the heavily doped p-type conduction behaviors observed for intrinsic n-type pyrite originates from strong Fermi level pinning due to surface defects. Such understanding allows us to develop strategies to mitigate these issues in order to improve the performance and eventually fulfill pyrite’s promise as a solar material. Furthermore, I will also show that the pyrite-phase of transition metal disulfides (MS₂, M= Fe, Co, Ni) on graphite disk substrates are highly efficient HER electrocatalysts.  Several morphologies of CoS₂, film, microwire, or nanowire, were controllably synthesized and these micro- and nanostructures with high surface areas substantially boost the catalytic performance.