RESUMO
The goal of photocatalytic CO2 reduction system is to achieve near 100 % selectivity for the desirable product with reasonably high yield and stability. Here, two-dimensional metal-organic frameworks are constructed with abundant and uniform monometallic active sites, aiming to be an emerged platform for efficient and selective CO2 reduction. As an example, water-stable Cu-based metal-organic framework nanoribbons with coordinatively unsaturated single CuII sites are first fabricated, evidenced by X-ray diffraction patterns and X-ray absorption spectroscopy. In situ Fourier-transform infrared spectra and Gibbs free energy calculations unravel the formation of the key intermediate COOH* and CO* is an exothermic and spontaneous process, whereas the competitive hydrogen evolution reaction is endothermic and non-spontaneous, which accounts for the selective CO2 reduction. As a result, in an aqueous solution containing 1â mol L-1 KHCO3 and without any sacrifice reagent, the water-stable Cu-based metal-organic framework nanoribbons exhibited an average CO yield of 82â µmol g-1 h-1 with the selectivity up to 97 % during 72â h cycling test, which is comparable to other reported photocatalysts under similar conditions.
RESUMO
Transition-metal sulfides boast a high theoretical capacity and have been regarded as a kind of prospective electrodes for supercapacitors; nevertheless, their inherent poor conductivity and low electrochemical active sites limit the practical applications of the materials.Herein, flower-like zinc cobalt sulfide (ZCS) microspheres with rich sulfur vacancies (ZCSδ) have been synthesized by a three-step procedure of hydrothermal, post-annealing and room-temperaturesulfuration treatments. The flower-like microspheres self-assembled by ultrathin nanosheets bring the active material fully contact with electrolyte, facilitating ion diffusion during charging and discharging. Furthermore, defect engineering of sulfur vacancies at the atomic level raises the intrinsic conductivity and increases active sites for electrochemical reactions. As a result, the obtained sulfur-deficient ZCS microspheres possess an excellent specific capacitance of 2709 F g-1 at 1 A g-1 and an exceptional cycling lifespan of maintaining 90.9% of the initial capacitance over 3000 cycles. In addition, the hybrid supercapacitor employing (HSC) sulfur-deficient flower-like ZCS microspheres as the positive electrode present a high energy density of 28 Wh kg-1 at the power density of 800 W kg-1. This investigation proposes an efficient strategy to significantly and synergistically enhance the electrochemical performance of the electrodes for hybrid supercapacitor by the comprehensive engineering of defect and morphology.