Optical Properties and Photocatalytic Performance of Si/TiO2 Tandem Semiconductor Microwire Slurries

Semiconductor particle suspension reactors hold promiseas a possiblelow-cost strategy for solar water-splitting, but they face severalchallenges that have inhibited their solar-to-hydrogen (STH) efficiencies.A tandem microparticle with a buried junction addresses some of thesechallenges and offers a pathway to high STH efficiency. As a slurry,the tandem microparticles need to be suspended and well dispersedwith maximum light absorption for a minimal photoactive particle concentration.Herein, proof-of-concept Ni/np(+)-Si/FTO/TiO2 tandemmicrowire structures capable of unassisted solar water-splitting wereinvestigated as a slurry using uplifting N-2 carrier gasbubbles. Transmittance, reflectance, and absorptance of the slurrywere characterized as a function of wavelength, bubble flowrate, andtandem microwire concentration using an integrating sphere. Notably,a slurry absorptance of 70-85% was achieved with only 1% ofthe solution volume filled with a photoactive material. Photochemicalactivity of the slurry was characterized with in situ monitoring ofthe photodegradation of methylene blue, including the effects of particleconcentration, bubble flowrate, spectral mismatch, intermixed lightscattering particles, and a back reflector.

Automated summary

Semiconductor particle suspension reactors hold promise for low-cost solar water-splitting, but their efficiency is hindered by challenges. Tandem microparticles with buried junctions offer a pathway to high efficiency. Experimental Ni/np(+)-Si/FTO/TiO2 tandem microwire structures achieved high slurry absorptance with minimal photoactive particle concentration.