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Published February 19, 2015 | Supplemental Material
Journal Article Open

Stable Solar-Driven Water Oxidation to O_2(g) by Ni-Oxide-Coated Silicon Photoanodes

Abstract

Semiconductors with small band gaps (<2 eV) must be stabilized against corrosion or passivation in aqueous electrolytes before such materials can be used as photoelectrodes to directly produce fuels from sunlight. In addition, incorporation of electrocatalysts on the surface of photoelectrodes is required for efficient oxidation of H_2O to O_2(g) and reduction of H_2O or H_2O and CO_2 to fuels. We report herein the stabilization of np^+-Si(100) and n-Si(111) photoanodes for over 1200 h of continuous light-driven evolution of O_2(g) in 1.0 M KOH(aq) by an earth-abundant, optically transparent, electrocatalytic, stable, conducting nickel oxide layer. Under simulated solar illumination and with optimized index-matching for proper antireflection, NiO_x-coated np+-Si(100) photoanodes produced photocurrent-onset potentials of −180 ± 20 mV referenced to the equilibrium potential for evolution of O_2(g), photocurrent densities of 29 ± 1.8 mA cm^(–2) at the equilibrium potential for evolution of O_2(g), and a solar-to-O_2(g) conversion figure-of-merit of 2.1%.

Additional Information

© 2015 American Chemical Society. Received: December 11, 2014; accepted: January 19. This work was supported through the Office of Science of the U.S. Department of Energy (DOE) under award no. DESC0004993 to the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub. UV−vis spectroscopy and atomic-force microscopy were performed at the Molecular Materials Research Center (MMRC) in the Beckman Institute at the California Institute of Technology. B.S.B. was supported by the Beckman Institute of the California Institute of Technology. A.C.N. was supported by a Graduate Research Fellowship from the National Science Foundation. M.R.S. was supported by a graduate fellowship from the Resnick Sustainability Institute. This work was additionally supported by the Gordon and Betty Moore Foundation under Award No. GBMF1225. We thank K. Walczak for providing the FTO coated np+-Si(100) samples, C. Koval, R. Liu, and M. Lichterman for stimulating discussions, N. Becerra and L. Zhou for their assistance with XRD measurements, and K. Papadantonakis for assistance with editing this manuscript.

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