Electrons and Hydroxyl Radicals Synergistically Boost the Catalytic Hydrogen Evolution from Ammonia Borane over Single Nickel Phosphides under Visible Light Irradiation

Abstract

From the perspective of tailoring the reaction pathways of photogenerated charge carriers and intermediates to remarkably enhance the solar‐to‐hydrogen energy conversion efficiency, we synthesized the three low‐cost semiconducting nickel phosphides Ni2P, Ni12P5 and Ni3P, which singly catalyzed the hydrogen evolution from ammonia borane (NH3BH3) in the alkaline aqueous solution under visible light irradiation at 298 K. The systematic investigations showed that all the catalysts had higher activities under visible light irradiation than in the dark and Ni2P had the highest photocatalytic activity with the initial turnover frequency (TOF) value of 82.7 min−1, which exceeded the values of reported metal phosphides at 298 K. The enhanced activities of nickel phosphides were attributed to the visible‐light‐driven synergistic effect of photogenerated electrons (e−) and hydroxyl radicals (.OH), which came from the oxidation of hydroxide anions by photogenerated holes. This was verified by the fluorescent spectra and the capture experiments of photogenerated electrons and holes as well as hydroxyl radicals in the catalytic hydrogen evolution process.

In situ formed nickel phosphide/iron oxide heterojunction for accelerating hydrogen generation

“…The abundant electrons around nickel favor the catalysis of NH 3 BH 3 hydrolysis. 27,30 The N 2 adsorption-desorption isotherm of the Fe 3 O 4 -Ni 2 P@C catalyst indicates a surface area of 72.9 m 2 g −1 with an average pore width of 13.0 nm (Fig. S17 and Table S3 †).…”

“…18,[23][24][25] In particular, nickel phosphide, an emerging noble-metal-free catalyst, displays high activity for NH 3 BH 3 hydrolysis. 26,27 Recent reports have demonstrated that catalysts with monometallic sites can be further improved by introducing a second metal to form dual active sites. This enhancement has been attributed to the synergistic effect of dual sites during the adsorption and dissociation of NH 3 BH 3 and H 2 O molecules.…”

Photocatalytic H2 Evolution from Ammonia Borane: Improvement of Charge Separation and Directional Charge Transmission

“…These results were consistent with the UV/Vis diffuse reflectance spectra. Considering that water might interact with photogenerated electrons during the AB hydrolysis reaction to enhance the photocatalytic H 2 evolution activity, [60] CoFeÀ Mo was also tested in photocatalytic H 2 evolution from AB (Figure 7a). However, no photocatalytic H 2 evolution activity was detected.…”