RESUMO
The electrochemical NRR to synthesize ammonia is considered as a promising method due to its approvable advantages of zero-pollution emission, feasible reaction proceedings, good safety and easy management. The multiple efforts have been devoted to the exploration of earth-abundant-element-based nanomaterials as high-efficiency electrocatalysts for realizing their industrial applications. Among these, the Ni-based nanomaterials is prioritized as an attractive non-noble-metal electrocatalysts for catalyzing NRR because they are earth-abundance and exceedingly easy to synthesize as well as also delivers the potential of high electrocatalytic activity and durability. In this review, after briefly elucidating the underlying mechanisms of NRR during the electrochemical process, we systematically sum up the recent research progress in representative Ni-based electrocatalysts, including monometallic Ni-based nanomaterials, bimetallic Ni-based nanomaterials, polymetallic Ni-based nanomaterials, etc. In particular, we discuss the effects of physicochemical properties, such as phases, crystallinity, morphology, composition, defects, heteroatom doping, and strain engineering, on the comprehensive performance of the abovementioned electrocatalysts, with the aim of establishing the nanostructure-function relationships of the electrocatalysts. In addition, the promising directions of Ni-based electrocatalysts for NRR are also pointed out and highlighted. The generic approach in this review may expand the frontiers of NRR and provides the inspiration for developing high-efficiently Ni-based electrocatalysts.
RESUMO
In this study, the synergistic behavior of Ni species and bimodal mesoporous undoped SnO2 is investigated in oxygen evolution reactions (OERs) under alkaline conditions without any other modification of the compositional phases or using noble metals. An efficient and environmentally friendly hydrothermal method to prepare bimodal mesoporous undoped SnO2 with a very high surface area (>130 m2 g-1) and a general deposition-precipitation method for the synthesis of well-dispersed Ni species on undoped SnO2 are reported. The powders were characterized by adsorption-desorption isotherms, TG-DTA, XRD, SEM, TEM, Raman, TPR-H2, and XPS. The best NiSn composite generates, under certain experimental conditions, a very high TOF value of 1.14 s-1 and a mass activity higher than 370 A g-1, which are remarkable results considering the low amount of Ni deposited on the electrode (3.78 ng). Moreover, in 1 M NaOH electrolyte, this material produces more than 24 mA cm-2 at an overpotential value of approximately +0.33 V, with only 5 wt % Ni species. This performance stems from the dual role of undoped SnO2, on the one hand, as a support for active and well-dispersed Ni species and on the other hand as an active player through the oxygen vacancies generated upon Ni deposition.
RESUMO
The tungsten carbide and cobalt-modified Ni-based catalyst [Ni-Co-WC/multiwall carbon nanotubes (MWCNTs)], synthesized through a sequential impregnation method, was evaluated for the urea electrooxidation in alkaline electrolyte to reduce the overpotential and increase the current density simultaneously. The as-prepared Ni-Co-WC/MWCNTs catalyst was characterized using scanning electron microscopy-EDX, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Characterization results indicate that Ni, Co, and WC nanoparticles are uniformly distributed on the MWCNTs. For the Ni-Co-WC/MWCNT electrode, the maximum current density for urea electrooxidation is more than 4 times higher than that of the Ni/C catalyst, with a reduction of 120 mV in the onset overpotential. In addition, the Ni-Co-WC/MWCNTs catalyst also shows an enhanced catalytic stability with a continuous higher current density under steady-state conditions.