Electronic Regulation of ZnCo Dual-Atomic Active Sites Entrapped in 1D@2D Hierarchical N-Doped Carbon for Efficient Synergistic Catalysis of Oxygen Reduction in Zn-Air Battery.

Transition metal-based nitrogen-doped carbon (M-Nx -C) is considered as a promising catalyst for the oxygen reduction reaction (ORR) in clean energy storage and conversion devices. Herein, ZnCo dual-atomic sites are incorporated in hierarchical N-doped carbon (HNC), with 1D nanotubes wrapped in 2D nanosheets structure (termed as 1D@2D ZnCo-HNC), via a one-step bio-inspired pyrolysis. The feeding ratio of Zn to Co precursor and pyrolytic temperature are critically modulated to achieve well-defined morphologies of the products, endowing them with the integrated merits of nanotubes and nanosheets as efficient ORR catalysts. Benefiting from the particular structure and electronic regulation of Zn on Co, the ZnCo-Nx dual-atomic system exhibits excellent ORR catalytic characteristics with an onset potential of 1.05 V and a half-wave potential of 0.82 V. Density functional theory calculations further explain the regulating role of Zn, such that the adjusted Co in ZnCo-Nx sites significantly reduces the energy cost to ultimately facilitate the ORR. Moreover, the Zn-air battery assembled with ZnCo-HNC is capable of delivering the maximum power density of 123.7 mW cm-2 and robust stability for 110 h (330 cycles). This method provides a promising strategy for fabricating efficient transition metal-based carbon catalysts for green energy devices.

Metal-Organic Framework-Derived Fe-Doped Co1.11 Te2 Embedded in Nitrogen-Doped Carbon Nanotube for Water Splitting.

A rational design is reported of Fe-doped cobalt telluride nanoparticles encapsulated in nitrogen-doped carbon nanotube frameworks (Fe-Co1.11 Te2 @NCNTF) by tellurization of Fe-etched ZIF-67 under a mixed H2 /Ar atmosphere. Fe-doping was able to effectively modulate the electronic structure of Co1.11 Te2 , increase the reaction activity, and further improve the electrochemical performance. The optimized electrocatalyst exhibited superior hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performances in an alkaline electrolyte with low overpotentials of 107 and 297 mV with a current density of 10 mA cm-2 , in contrast to the undoped Co1.11 Te2 @NCNTF (165 and 360 mV, respectively). The overall water splitting performance only required a voltage of 1.61 V to drive a current density of 10 mA cm-2 . Density function theory (DFT) calculations indicated that the Fe-doping not only afforded abundant exposed active sites but also decreased the hydrogen binding free energy. This work provided a feasible way to study non-precious-metal catalysts for an efficient overall water splitting.