Enhanced Electrocatalytic Water Oxidation by Interfacial Phase Transition and Photothermal Effect in Multiply Heterostructured Co₉S₈/Co₃S₄/Cu₂S Nanohybrids

Abstract

The rational design of advanced nanohybrids (NHs) with optimized interface electronic environment and rapid reaction kinetics is pivotal to electrocatalytic schedule. Herein, we developed a multiple heterogeneous Co9S8/Co3S4/Cu2S nanoparticle in which Co3S4 germinates between Co9S8 and Cu2S. Using high‐angle annular‐dark‐field imaging and theoretical calculation, it was found that the integration of Co9S8 and Cu2S tends to trigger the interface phase transition of Co9S8, leading to Co3S4 interlayer due to the low formation energy of Co3S4/Cu2S (−7.61 eV) than Co9S8/Cu2S (−5.86 eV). Such phase transition not only lowers the energy barrier of oxygen evolution reaction (OER, from 0.335 eV to 0.297 eV), but also increases charge carrier density (from 7.76×1014 to 2.09×1015 cm−3), and creates more active sites. Compared to Co9S8 and Cu2S, the Co9S8/Co3S4/Cu2S NHs also demonstrate notable photothermal effect that can heat the catalyst locally, offset the endothermic enthalpy change of OER, and promote carrier migrate, reaction intermediates adsorption/deprotonation to improve reaction kinetics. Profiting from these favorable factors, the Co9S8/Co3S4/Cu2S catalyst only requires an OER overpotential of 181 mV and overall water splitting cell voltage of 1.43 V to driven 10 mA cm−2 under the irradiation of near‐infrared light, outperforming those without light irradiation and many reported Co‐based catalysts.

Preparation of Cu(OH)2/Cu2S arrays for enhanced hydrogen evolution reaction

“…According to the XPS spectrum of S 2p in Figure 5C, the signal peaks of 161.4, 162.4, and 163.4 eV belong to S 2p 3/2 , S 2p 1/2 , S = S, and satellite peaks on the surface of the material, respectively, where the S 2p 1/2 binding energy is caused by the metal–sulfur bond. The S 2p 3/2 binding energy is due to the low coordination of S 2− 52,53 . In Figure 5D, it can be seen that the high‐resolution O 1 s peaks are divided into three overlapping peaks.…”

“…The S 2p 3/2 binding energy is due to the low coordination of S 2− . 52,53 In Figure 5D, it can be seen that the high-resolution O 1 s peaks are divided into three overlapping peaks. The three peaks of O 1 s at 530.34, 531.47, and 533 eV belong to M-O bond, defect site, and −OH group, respectively.…”