ABSTRACT
The use of organic molecules represents a very attractive and promising alternative for electrical energy storage applications. Quinones, in general, and anthraquinones, in particular, are especially attractive due to their ability to reversibly exchange multiple electrons per formula unit. When used as the active electrode material in a real lithium-ion battery (LIB), crystalline anthraquinone powders reversibly change crystal packing as a function of state-of-charge (redox state), with well-defined voltage plateaus appearing concomitantly with new phases. Operando powder X-ray diffraction (XRD) is a powerful method for screening the structural stability of organic cathode candidates and for understanding electrochemically-induced structural transformations within organic molecular crystals. Herein we explore the electrochemical lithiation-induced polymorphism of anthraquinone (AQ) and three related derivatives. We believe that this analysis can serve as a model for studying organic charge storage within crystalline small-molecule candidates.
ABSTRACT
Molybdenum and tungsten diselenide are among the most robust and efficient semiconductor materials for photoelectrochemistry, but they have seen limited use for integrated solar energy storage systems. Herein, we report that n-type WSe2 photoelectrodes can facilitate unassisted aqueous HI electrolysis to H2(g) and HI3(aq) when placed in contact with a platinum counter electrode and illuminated by simulated sunlight. Even in strongly acidic electrolyte, the photoelectrodes are robust and operate very near their maximum power point. We have rationalized this behavior by characterizing the n-WSe2|HI/HI3 half cell, the Pt|HI/H2||HI3/HI|Pt full cell, and the n-WSe2 band-edge positions. Importantly, specific interactions between the n-WSe2 surface and aqueous iodide significantly shift the semiconductor's flatband potential and allow for unassisted HI electrolysis. These findings exemplify the important role of interfacial chemical reactivity in influencing the energetics of semiconductor-liquid junctions and the resulting device performance.
