Iron Active Center Coordination Reconstruction in Iron Carbide Modified on Porous Carbon for Superior Overall Water Splitting.

In this work, a novel liquid nitrogen quenching strategy is engineered to fulfill iron active center coordination reconstruction within iron carbide (Fe3C) modified on biomass-derived nitrogen-doped porous carbon (NC) for initiating rapid hydrogen and oxygen evolution, where the chrysanthemum tea (elm seeds, corn leaves, and shaddock peel, etc.) is treated as biomass carbon source within Fe3C and NC. Moreover, the original thermodynamic stability is changed through the corresponding force generated by liquid nitrogen quenching and the phase transformation is induced with rich carbon vacancies with the increasing instantaneous temperature drop amplitude. Noteworthy, the optimizing intermediate absorption/desorption is achieved by new phases, Fe coordination, and carbon vacancies. The Fe3C/NC-550 (550 refers to quenching temperature) demonstrates outstanding overpotential for hydrogen evolution reaction (26.3 mV at -10 mA cm-2) and oxygen evolution reaction (281.4 mV at 10 mA cm-2), favorable overall water splitting activity (1.57 V at 10 mA cm-2). Density functional theory (DFT) calculations further confirm that liquid nitrogen quenching treatment can enhance the intrinsic electrocatalytic activity efficiently by optimizing the adsorption free energy of reaction intermediates. Overall, the above results authenticate that liquid nitrogen quenching strategy open up new possibilities for obtaining highly active electrocatalysts for the new generation of green energy conversion systems.

g-C3N4-wrapped nickel doped zinc oxide/carbon core-double shell microspheres for high-performance photocatalytic hydrogen production.

The development of efficient heterojunctions with enhanced photocatalytic properties is considered a promising approach for photocatalytic hydrogen production. In this study, graphitic carbon nitride (g-C3N4)-wrapped nickel-doped zinc oxide/carbon (Ni-ZnO@C/g-C3N4) core-double shell heterojunctions with unique core-double shell structures were employed as efficient photocatalysts through an innovative approach. Ni doping can enhance the intensity and range of visible light absorption in ZnO, and the carbon core coupled with the hollow double-shell structure can accelerate the charge transfer rate and improve the photon utilization efficiency. Meanwhile, the construction of the Z-scheme heterojunction extended the electron-hole pair transport path. In addition, the Z-scheme charge-transfer mechanism of Ni-ZnO@C/g-C3N4 under simulated sunlight was verified by photoluminescence (PL) and electron spin resonance (ESR) experiments. As a result, the obtained photocatalyst acquired a high hydrogen evolution rate of 336.08 µmol g-1h-1, which is 36.49 times higher than that of pristine ZnO. Overall, this work may provide a pathway for the construction of highly efficient photocatalysts with unique core-double shell structures.