Space charge transfer is crucial for an efficient electrocatalytic process, especially for narrow-band-gap metal sulfides/selenides. Herein, we designed and synthesized a core–shell structure which is an ultrathin MoSe2 nanosheet coated CuS hollow nanoboxes (CuS@MoSe2) to form an open p–n junction structure. The space charge effect in the p–n junction region will greatly improve electron mass transfer and conduction, and also have abundant active interfaces. It was used as a bifunctional electrocatalyst for water oxidation at a wide pH range. It exhibits a low overpotential of 49 mV for the HER and 236 mV for the OER at a current density of 10 mA·cm –2 in acidic pH, 72 mV for the HER and 219 mV at 10 mA·cm –2 for the OER in alkaline pH, and 62 mV for the HER and 230 mV at 10 mA·cm –2 for the OER under neutral conditions. The experimental results and density functional theory calculations testify that the p–n junction in CuS@MoSe2 designed and synthesized has a strong space charge region with a synergistic effect. The built-in field can boost the electron transport during the electrocatalytic process and can stabilize the charged active center of the p–n junction. This will be beneficial to improve the electrocatalytic performance. This work provides the understanding of semiconductor heterojunction applications and regulating the electronic structure of active sites.
Electrocatalysts based on precious metals of Pt, Ir, Ru, and their oxides are considered to be the most effective materials for accelerating the water oxidation process, but the high cost and scarcity limited the large-scale applications. Therefore, it is necessary to develop efficient, low-cost, and durable electrocatalysts to replace precious metal catalysts. [3] As we know, in the electrocatalytic reaction of two electrons and four electrons, the activation of H 2 O and the adsorption of reaction intermediates by the active site are essential. [2b,4] For OER, the kinetic rate may be limited by the weak oxygen-binding state of the metal, and the strong bonding ability may limit the proton-electron transfer to *OH and *O. [5] On the other hand, the Volmer-Heyrovsky step will be limited by the weak or strong bonding ability during HER. [6] According to the above discussion, the adsorption capacity of the active site to reaction intermediates plays a crucial role in electrocatalytic performance, the weaker and stronger adsorption capacity will also have an adverse impact on the activity of electrocatalysis. Hence, the construction of customizable electronic structures for efficient bifunctional electrocatalysts is irresistibly attractive but still challenging.Among various electrocatalysts, metallic phthalocyanine compounds (MPc, M = Fe, Co, Ni Cu, etc.) have many advantages Implementing a molecular modulation strategy for metallic phthalocyanines (MPc) without losing the activity of the metal center and inducing a multifunction characteristic in electrocatalytic remains a challenge. Herein, a series of 2D CuCo bimetallic polymerized phthalocyanine modified with strong electron-withdrawing groups (CuCoPc-g, g = F, Cl, Br, NO 2 ) for water oxidation in the alkaline electrolyte is designed and simply synthesized. The experimental results testify that the bimetallic design can perform electronic adjustment once and introduce the second active sites to get bifunctional characteristics, and then the electronic structure of the active center can be regulated by electron-withdrawing groups for a second time to achieve the optimal state. These electrons that transfer in the active center of inner metal can generate space-charged regions and the design of the polymer can stabilize active site region to maintain long-term electrolytic stability and high activity. This study precisely regulates the electronic structure of MPc at the molecular level and provides insight into the multifunctional design of polymeric macrocyclic electrocatalysts.
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