Spontaneous mesostructure formation produces optically transmissive Ni-P films that are catalytically active for the photoelectrochemical hydrogen evolution reaction

Ni-P films that are catalytically active for the hydrogen-evolution reaction were electrodeposited onto photoactive Si substrates between 20 °C and 80 °C from an aqueous solution. Ni-P films deposited at 20 °C and exposed to acidic environments spontaneously developed deep cracks. A substantial increase in optical transmission to the semiconducting substrate resulted without affecting the catalytic performance of the film. In contrast, Ni-P films deposited at 80 °C only developed minor surface-level cracks and did not exhibit a substantial increase in optical transmission. During electrodeposition of the Ni-P films at low temperatures, the uptake of parasitically evolved hydrogen generated partially defective Ni-P, causing crack formation. Increases in the temperature of the electrodeposition bath increased the faradaic efficiency of Ni-P deposition and consequently reduced the uptake of parasitically generated hydrogen. The defective Ni-P films were converted to a crack-resistant material by thermally desorbing the excess hydrogen that was absorbed during the low-temperature electrodeposition process. Ni-P films that are catalytically active for the hydrogen-evolution reaction were electrodeposited onto photoactive Si substrates between 20 °C and 80 °C.