Single‐Site Active Cobalt‐Based Photocatalyst with a Long Carrier Lifetime for Spontaneous Overall Water Splitting

Abstract

An active and stable photocatalyst to directly split water is desirable for solar‐energy conversion. However, it is difficult to accomplish overall water splitting without sacrificial electron donors. Herein, we demonstrate a strategy via constructing a single site to simultaneously promote charge separation and catalytic activity for robust overall water splitting. A single Co1‐P4 site confined on g‐C3N4 nanosheets was prepared by a facile phosphidation method, and identified by electron microscopy and X‐ray absorption spectroscopy. This coordinatively unsaturated Co site can effectively suppress charge recombination and prolong carrier lifetime by about 20 times relative to pristine g‐C3N4, and boost water molecular adsorption and activation for oxygen evolution. This single‐site photocatalyst exhibits steady and high water splitting activity with H2 evolution rate up to 410.3 μmol h−1 g−1, and quantum efficiency as high as 2.2 % at 500 nm.

Single Metal Atom Photocatalysis

“…In addition, the single Co site was favorable for absorbing and activating H 2 O, which facilitated the rate‐limited oxygen evolution reaction for water splitting. Therefore, the obtained Co 1 ‐phosphide/P‐doped g‐C 3 N 4 exhibited exceptionally high water‐splitting activity with a quantum efficiency of 2.2% at 500 nm …”

“…As another promising photocatalyst, g‐C 3 N 4 possesses excellent visible light absorption, high stability, and capability to provide abundant N donor atoms to trap highly active metal atoms. Thus, it has been extensively explored as a support to anchor various metal atoms, including noble metal atoms (Pt, Pd, Ag) and nonprecious metal atoms (Al, Co). By a simple liquid‐phase reaction with g‐C 3 N 4 and H 2 PtCl 6 followed by annealing at a low temperature, Xie and co‐workers embedded single Pt atoms on the top of the five‐membered rings of the g‐C 3 N 4 network through PtC and PtN bonds .…”

“…Single nonprecious metal atoms, such as Al and Co, have also been successfully embedded on the surface of g‐C 3 N 4 . Cao et al constructed atomically dispersed Co atoms on g‐C 3 N 4 using the ALD method followed by O 3 treatment .…”

“…Therefore, the as‐prepared photocatalyst showed an excellent photocatalytic activity with hydrogen evolution rate achieving 10.8 µmol h −1 , which was 11 times higher than that of pristine g‐C 3 N 4 . Liu et al reported that a single‐site Co 1 ‐phosphide configuration was obtained by the strong confinement of g‐C 3 N 4 and phosphidation . X‐ray absorption and photoelectron spectroscopy results revealed that the atomically dispersed Co atoms were anchored on the P‐doped g‐C 3 N 4 matrix, forming a Co 1 –P 4 structure .…”

“…Liu et al reported that a single‐site Co 1 ‐phosphide configuration was obtained by the strong confinement of g‐C 3 N 4 and phosphidation . X‐ray absorption and photoelectron spectroscopy results revealed that the atomically dispersed Co atoms were anchored on the P‐doped g‐C 3 N 4 matrix, forming a Co 1 –P 4 structure . The mid‐gap states introduced by the P dopants in g‐C 3 N 4 not only extended the light absorption range, but also acted as separation centers to trap temporarily photoexcited electrons from the conduction band of P‐doped g‐C 3 N 4 .…”