Advanced bi-functional CoPi co-catalyst-decorated g-C₃N₄ nanosheets coupled with ZnO nanorod arrays as integrated photoanodes

Abstract

In this work, a CoPi-decorated type II heterojunction composed of one-dimensional (1D) ZnO nanorod arrays (NRAs) coated with two-dimensional (2D) carbon nitride (g-C3N4) was successfully prepared and used as photoanode. CoPi has been speculated to be a mixture of amorphous compound and two cobalt-based compounds: Co3(PO3)6·14H2O and Co(H2PO2)2·6H2O. The advanced bi-functional CoPi acts like a shelter, effectively inhibiting the photocorrosion of CNNS/ZnO NRAs and providing a faster hole transfer channel. Synergistic effects at the interface of the heterojunction efficiently improve the separation of charge carriers from photoexcited g-C3N4 nanosheets to the ZnO nanorods. Photocurrent density is also greatly enhanced by loading CoPi on CNNS/ZnO NRAs heterojunction. The maximum photocurrent density (2.45 mA cm-2 at 1.23 V vs. RHE) generated from CoPi(10)-CNNS(600)/ZnO nanorods is about 10.2 times greater than that of pristine ZnO nanorods (0.24 mA cm-2 at 1.23 V vs. RHE) and 2.5 times higher than that of CNNS(800)/ZnO (0.95 mA cm-2 at 1.23 V vs. RHE). The further increase of photoelectrocatalytic performance may be attributed to CoPi relieving the charge accumulation at the semiconductor/electrolyte, which decreases the electron-hole recombination rate.

Graphitic carbon nitride (g‐C3N4)‐based nanosized heteroarrays: Promising materials for photoelectrochemical water splitting

“…For example, a novel Co‐Pi decorated type II ZnO/g‐C 3 N 4 NS NRA has been successfully prepared and used as photoanode (Figure 6H). 118 Similar to its effect on TiO 2 /g‐C 3 N 4 heteroarray, 114 Co‐Pi in this system can also provide a fast hole‐transfer channel from photoelectrode materials to electrolytes, thus leading to a suppressed recombination of photogenerated electrons/holes. As a result, the Co‐Pi modified ZnO/g‐C 3 N 4 NS NRA photoanode produces the higher photocurrent density (2.45 mA cm −2 at 1.23 V vs RHE) than that of the photoanode without Co‐Pi cocatalyst (0.95 mA cm −2 at 1.23 V vs RHE) under AM 1.5 G irradiation (Figure 6I and Table 1).…”

“…Similar to TiO 2 ; nevertheless, the poor light absorption and high recombination probability of photogenerated charges also impair the PEC performance of ZnO‐based photoanodes 139,140 . Recently, ZnO arrays have been decorated by g‐C 3 N 4 to develop the ZnO/g‐C 3 N 4 heteroarrays for the enhanced solar light harvesting and accelerated exciton separation 116‐121 . For example, a ZnO NRA has been decorated by g‐C 3 N 4 through simple reflux and TVC process (Figure 6A).…”

“…(I) LSV curves with different samples. (Reproduced with permission: Copyright 2018, the Royal Society of Chemistry 118 …”

“…139,140 Recently, ZnO arrays have been decorated by g-C 3 N 4 to develop the ZnO/g-C 3 N 4 heteroarrays for the enhanced solar light harvesting and accelerated exciton separation. [116][117][118][119][120][121] For example, a ZnO NRA has been decorated by g-C 3 N 4 through simple reflux and TVC process (Figure 6A). 116 The ZnO/g-C 3 N 4 composite photoanode exhibits an ordered one-dimensional (1D) NRA morphology, which is very helpful for the rapid transport of photogenerated electrons (Figure 6B).…”

“…For other improved strategies, the cocatalysts have been adopted to develop the high-performance ZnO/g-C 3 N 4 heteroarray photoanodes, including Co-Pi 118,119 and Pt. 120 For example, a novel Co-Pi decorated type II ZnO/ g-C 3 N 4 NS NRA has been successfully prepared and used as photoanode (Figure 6H).…”