Efficient, earth-abundant transition metal photocatalysts for hydrogen evolution are under intense development. Two major hurdles for the photocatalytic function of these materials are their relatively low energy conversion efficiency and low photostability. To improve the energy conversion efficiency, a deeper understanding of the charge transport and the recombination mechanisms of the light-excited electron-hole pairs is necessary. To improve electron transport and prevent carrier recombination organic ligands are widely used to passivate the surface of transition metal semiconductors in photovoltaic applications. However, the passivation effect and the underlying mechanisms have been rarely explored in the context of photocatalytic materials that operate in aqueous milieus. We discovered that films of bacterially precipitated CdS nanoparticles exhibit i) carrier lifetimes that are substantially longer and exhibit ii) photocurrent densities that are higher compared to those in films prepared from unpassivated, chemically synthesized CdS nanoparticles. We hypothesized that these properties arise from passivation through cysteine which was added as the sulfur source in the bacterial precipitation process. To further understand the passivation effect and its underlying mechanism, we tested the effect of binding group and head group chemistry on PEC photocurrent density and catalyst stability. We anticipate that our findings will advance the rational design and the performance of biosynthesized transition metal sulfide photocatalysts.

Organic ligands enhance the recombination lifetime and photoelectrochemical performance of biosynthesized CdS nanoparticle thin films

256th National Meeting (2018)

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