Ultrasmall Cocatalyst Nanoparticles for Efficient Photoelectrocatalysis: Optical Properties and Electrolyte Effects
Dariusz Mitoraj a, Radim Beranek a
Materials for Sustainable Development Conference (MATSUS)
Proceedings of nanoGe September Meeting 2017 (NFM17)
SF1: Material and Device Innovations for the Practical Implementation of Solar Fuels (SolarFuel17)
Barcelona, Spain, 2017 September 4th - 9th
Organizers: Wilson Smith and Ki Tae Nam
Oral, Dariusz Mitoraj, presentation 116
Publication date: 20th June 2016

The coupling of light absorbers to cocatalysts is of fundamental importance for efficient solar-driven photoelectrocatalytic water splitting.1,2 Recently we achieved effective loading of visible light-active porous hybrid TiO2-PH (PH – polyheptazine, “graphitic carbon nitride”) photoanodes for water photooxidation with ultrasmall (~1-2 nm), highly disordered CoO(OH)x nanoparticles using a two-step impregnation method.3 Under visible light (λ > 420 nm) irradiation, the resulting photoanodes significantly outperformed photoanodes loaded with conventional cobalt-based cocatalyst (Co-Pi) comprising larger nanoparticles (~5 nm) both in terms of Faradaic efficiency of oxygen evolution (by the factor of 2) and performance stability under long-term irradiation.

The contribution will focus on elucidating the advantages of using ultrasmall CoO(OH)x nanoparticles as cocatalysts. Specifically, due to their high transparency in visible range, higher loading of porous photoanodes with cobalt catalytic sites could be achieved, while the photocurrent losses due to parasitic light absorption by the cocatalyst are minimized. Importantly, EXAFS data recorded before and after photoelectrocatalysis indicated that the significant enhancement in stability of ultrasmall CoO(OH)x nanoparticles in borate as compared to phosphate electrolytes can be explained by the difference in structural ordering dictated by interaction of the electrolyte anions with cobalt ions.

The impact of structural and optical properties of cocatalysts as well as the strong influence of the electrolyte composition on the activity and stability of photoelectrocatalytic systems comprising transition metal oxide electrocatalysts will be discussed in detail.

References

[1] M. Bledowski, L. Wang, S. Neubert, D. Mitoraj, R. Beranek, J. Phys. Chem., 2014, 118, 18951-18961.

[2] O. Khavryuchenko, L. Wang, D. Mitoraj, G. H. Peslherbe, R. Beranek, J. Coord. Chem., 2015, 68, 3317-3327.

[3] L. Wang, D. Mitoraj, O. V. Khavryuchenko, S. Turner, T. Jacob, R. Hockling, R. Beranek, ACS Catal. 2017, submitted.

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