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)

Abstract

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 H 2 SO 4 (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 (η 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 η = 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.

Scalability and feasibility of photoelectrochemical H2evolution: the ultimate limit of Pt nanoparticle as an HER catalyst

“…Additionally, Pt is known to be highly durable in the acidic environments used in electrolysers or PEC devices. 18 These high loadings of CoP drastically reduced the photocurrent density due to parasitic light absorption decreasing the overall efficiency of the Sibased photocathode. 2 This is due to the lower current densities of 5 -20 mA/cm 2 , which PEC devices will operate at due to solar flux limitations.…”

“…15 While a low Tafel slope is certainly an important requirement for HER catalysts used in electrolysers, typically operated at high current densities (~A/cm 2 ), in photoelectrocatalytic devices high Pt exchange current density appears to be a more important criterion when chosen the HER catalyst. 18 While this might not be an issue for small band gap photocathodes on the backside of a monolithic device, the efficiency will be limited in a design with a large band gap photocathode and Pt appears to be still the optimal choice for HER catalysts in these PEC devices. Furthermore, it is often neglected in the development of efficient PEC devices that catalysts (HER or OER) will absorb light reducing the light limited current density provided by the photon absorber.…”

Control of the Band-Edge Positions of Crystalline Si(111) by Surface Functionalization with 3,4,5-Trifluorophenylacetylenyl Moieties

“…1 Modern semiconductor devices rely heavily on p-n homojunctions to form a voltageproducing junction that is independent of the energetics of the interfacing phase, which can include metals, 2-3 metal oxides, [4][5][6][7][8] catalysts, [9][10] conductive polymers, [11][12][13][14] and electrolytes. [15][16][17] Many semiconductors cannot, however, be doped to form high-quality p-n homojunctions, and moreover the diffusive doping processes used to fabricate emitter layers is generally not compatible with small-grain-size polycrystalline thin-film semiconducting base layers.…”

Functional integration of Ni–Mo electrocatalysts with Si microwire array photocathodes to simultaneously achieve high fill factors and light-limited photocurrent densities for solar-driven hydrogen evolution

“…19 Si microwire arrays, however, do not absorb a large proportion of incoming, normally incident photons on the ''first pass'' of such photons through the structure of the device. 8 As a result, significant parasitic optical absorption occurs in such devices even with the catalyst film deposited exclusively at the base of the array.…”