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.
ASJC Scopus subject areas
- Environmental Chemistry
- Renewable Energy, Sustainability and the Environment
- Nuclear Energy and Engineering