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Published November 2012 | Supplemental Material
Journal Article Open

Hydrogen-evolution characteristics of Ni–Mo-coated, radial junction, n+p-silicon microwire array photocathodes


The photocathodic H_2-evolution performance of Ni–Mo-coated radial n+p junction Si microwire (Si MW) arrays has been evaluated on the basis of thermodynamic energy-conversion efficiency as well as solar cell figures of merit. The Ni–Mo-coated n^(+)p-Si MW electrodes yielded open-circuit photovoltages (V_oc) of 0.46 V, short-circuit photocurrent densities (J_sc) of 9.1 mA cm^(−2), and thermodynamically based energy-conversion efficiencies (η) of 1.9% under simulated 1 Sun illumination. Under nominally the same conditions, the efficiency of the Ni–Mo-coated system was comparable to that of Pt-coated n+p-Si MW array photocathodes (V_oc = 0.44 V, J_sc = 13.2 mA cm^(−2_, η = 2.7%). This demonstrates that, at 1 Sun light intensity on high surface area microwire arrays, earth-abundant electrocatalysts can provide performance comparable to noble-metal catalysts for photoelectrochemical hydrogen evolution. The formation of an emitter layer on the microwires yielded significant improvements in the open-circuit voltage of the microwire-array-based photocathodes relative to Si MW arrays that did not have a buried n^(+)p junction. Analysis of the spectral response and light-intensity dependence of these devices allowed for optimization of the catalyst loading and photocurrent density. The microwire arrays were also removed from the substrate to create flexible, hydrogen-evolving membranes that have potential for use in a solar water-splitting device.

Additional Information

© 2012 Royal Society of Chemistry. Received 16 August 2012; Accepted 13 September 2012; First published on the web 08 October 2012. ELW and NSL acknowledge support from the Department of Energy (DE-FG02-05ER15754) for Si MW growth and device fabrication. JRM and HBG acknowledge support from the National Science Foundation (NSF) Powering the Planet Center for Chemical Innovation (CHE-0802907) for catalyst preparation and characterization. The authors would like to thank Hal Emmer, Dan Turner-Evans, and Elizabeth Santori for help with device fabrication and spectral response data collection. We acknowledge critical support and infrastructure provided for this work by the Kavli Nanoscience Institute at Caltech. JRM would like to thank the Department of Energy, Office of Science, for a graduate research fellowship.

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