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 (ff) of 0.24, and an ideal regenerative cell efficiency (_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 = 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.