In situ electrochemical APXPS analysis of ALD grown Cu catalyst for CO2 reduction

The grand challenge in artificial photosynthesis is to produce liquid solar fuels from water and carbon dioxide. Unfortunately, current materials solutions for a photocatalytic (PEC) solar fuel reactor lack efficiency, selectivity towards liquid fuel products, and long-term stability. Cu based catalysts are so far the most promising materials for the carbon dioxide reduction reaction (CO2RR), whereas the selectivity of Cu catalyst towards liquid products is strongly affected by the exact chemical composition and structure. Recently, Eilert et al. suggested, based on in situ electrochemical APXPS measurements on Cu foil, that the high activity of oxide-derived copper towards CO2RR stems from subsurface oxygen that was proposed to increase the CO binding energy and thus enhance the production of methanol and multicarbon products [1]. This contradicts the alternative hypothesis that assigns the activity to Cu2O on the surface, albeit no copper oxide should be stable at reductive CO2RR conditions.

In this work, ALD grown Cu oxide thin film was analyzed in situ by electrochemical APXPS at the HIPPIE beamline, MAX IV Laboratory. The results, highlighted in Figure 1, show similar oxygen species on reduced ALD Cu oxide thin film to what was assigned to subsurface oxygen in Ref. [1]. Therefore, the ALD grown Cu oxide thin film is considered as a promising catalyst coating for photocathodes in PEC solar fuel reactors.

[1] A. Eilert, F. Cavalca, F.S. Roberts, J. Osterwalder, C. Liu, M. Favaro, E.J. Crumlin, H. Ogasawara, D. Friebel, L.G.M. Pettersson, A. Nilsson, J. Phys. Chem. Lett. 8 (2017) 285–290.