Comparison of the Performance of CoP-Coated and Pt-Coated Radial Junction n+p-Silicon Microwire-Array Photocathodes for the Sunlight-Driven Reduction of Water to H2(g)

The electrocatalytic performance for hydrogen evolution has been evaluated for radial-junction n(+)p-Si microwire (MW) arrays with Pt or cobalt phosphide, CoP, nanoparticulate catalysts in contact with 0.50 M H2SO4(aq). The CoP-coated (2.0 mg cm(-2)) n(+)p-Si MW photocathodes were stable for over 12 h of continuous operation and produced an open-circuit photovoltage (V-oc) of 0.48 V, a light-limited photocurrent density (J(ph)) of 17 mA cm(-2), a fill factor (if) of 0.24, and an ideal regenerative cell efficiency (eta(IRC)) of 1.9% under simulated 1 Sun illumination. Pt-coated (0.5 mg cm(-2)) n(+)p-Si MW-array photocathodes produced V-oc = 0.44 V, J(ph) = 14 mA cm(-2), ff = 0.46, and eta = 2.9% under identical conditions. Thus, the MW geometry allows the fabrication of photocathodes entirely comprised of earth-abundant materials that exhibit performance comparable to that of devices that contain Pt.