Engineering Morphology and Electron Redistribution of a Ni/WO3 Mott-Schottky Bifunctional Electrocatalyst for Efficient Alkaline Urea Splitting

Construction of the desired morphology and nanointerface to expose the active sites and modulate the electronic structure offers an effective approach to boosting urea splitting for energy-saving hydrogen generation. Herein, we fabricate a Ni/WO3 Mott-Schottky heterojunction electrocatalyst with a hedgehog-like structure supported on Ni foam toward alkaline urea splitting. Different Ni/WO3 morphologies, such as microspheres, hedgehog-like structures, octahedrons, and cubes, were obtained when various ratios of Ni/W feeds were used. The Mott-Schottky nanointerfaces between Ni and WO3 domains are visually confirmed by high-resolution transmission electron microscopy images, which also accelerated the charge transfer rate. Benefiting from the high electrochemically active surface area and enhanced charge transferability, the optimal Ni/WO3 electrode exhibits outstanding catalytic activity toward hydrogen generation with a low overpotential of 163 mV at 100 mA cm-2 in alkaline solution and reduced cell voltage of 1.67 V when coupled with urea oxidation reaction. Theoretical calculations reveal that the Ni sites in Ni/WO3 optimize the H adsorption energy (ΔGH*) with the |ΔGH*| value of 0.097 eV, much lower than that of Ni (0.35 eV) and WO3 (0.235 eV). This work demonstrates important guidance in designing an efficient electrocatalyst for urea splitting.

Synergetic of Built-In Electric Field and Sulfur Defects in Co@Co9S8 Mott-Schottky To Achieve High-Efficiency Zinc-Air Battery Performance

The slow kinetics of the bifunctional (OER/ORR) oxygen electrocatalyst is the bottleneck problem restricting the performance of zinc-air batteries (ZABs). The design and synthesis of an efficient and stable electrocatalyst at the air cathode to improve the performance of ZABs is of great significance for the development of sustainable energy conversion devices. Herein, we have developed a sulfur vacancy-rich Mott-Schottky catalyst (Co@Co₉S₈-NCNT), which shows superior ORR/OER bifunctional electrochemical activity and stability. Specifically, the OER overpotential is only 210 mV at 10 mA cm^-2, and the half-wave potential (E_1/2) of ORR is up to 0.88 V. Furthermore, a ZAB has been assembled using the Co@Co₉S₈-NCNT, which delivers a high power density (196.7 mW cm^-2) and an open-circuit voltage (1.501 V), showing excellent battery performance. Density functional theory calculations demonstrate that the Co@Co₉S₈ Mott-Schottky heterojunction and S vacancy defects are beneficial to elevate the d-band central energy level to the Fermi level, significantly enhancing the adsorption/desorption capacity of oxygen-containing intermediates, thereby effectively improving the OER activity. Moreover, the N-doped carbon nanotubes can promote the continuous electron transfer between the metal and semiconductor interface. This work proposes a valid method for the construction and structural regulation of Mott-Schottky catalysts and offers new insights into the development of catalytic materials for energy conversion equipment.

Synergetic Nanoarchitectonics of Defects and Cocatalysts in Oxygen-Vacancy-Rich BiVO4/reduced graphene oxide Mott-Schottky Heterostructures for Photocatalytic Water Oxidation

Water oxidation process is a pivotal step of photosynthesis and stimulates the progress of high-performance catalysts for renewable fuel production. Despite the performance benefit of cocatalysts, defect engineering holds promise to settle inherent limitations of semiconductors aiming at sluggish water oxidation. Here, we modify the in situ growth pathway of monoclinic BiVO₄ (m-BiVO₄) on reduced graphene oxide (rGO), constructing abundant surface oxygen vacancies (O_V)-incorporated m-BiVO₄/rGO heterostructure toward water oxidation reaction under visible light. Owing to the O_V in the m-BiVO₄ component, a vacancy-related defect level allows more electrons to be photoexcited by low-energy photons to cause the electron transition, boosting photoabsorption as well as photoexcitation. Besides, the O_V can reinforce surface adsorption and reduce the dissociation energy of water molecules. Particularly because of the synergy of O_V and cocatalyst rGO, the O_V functions as electron-trapped sites to facilitate the carrier separation; the rGO not only receives electrons from m-BiVO₄ promoted by internal electric field over Mott-Schottky heterostructures but also spurs further electron diffusion along a highly conductive carbon network. These merits enable the O_V-incorporated m-BiVO₄/rGO heterostructure with an over 209% growth in O₂ yield relative to the counterpart. The increased performance is also validated by the significant rise of ^•OH radicals and ^•O₂^- radicals. The current work paves a novel avenue for the integration of defect engineering and cocatalyst coupling in artificial photosynthesis.