Coupling Dual-phased nickel selenides with N-doped carbon enables efficient urea electrocatalytic oxidation.

Electrochemical urea oxidation reaction (UOR) is urgently in demand for diverse energy conversion and storage device coupled with pollution treatment because of its favorable thermodynamic potential (0.37 V vs RHE) and wide distribution nature of urea, but simultaneously gravely limited by the sluggish reaction dynamics and poisoning of catalyst. Herein, dual-phased Ni0.85Se/NiSe2 coupling with N doped carbon (Ni0.85Se/NiSe2@NC-2) in situ is prepared by a solvothermal-selenization pathway. Benefiting from the collective promotion of the dual-phased composition and the NC support, Ni0.85Se/NiSe2@NC provides abundant active sites, enhanced electrical conductivity. It delivers a current density of 252 mA cm-2 at 1.6 V vs RHE with a small Tafel slop of 64.4 mV dec-1 and gets a lower reaction barrier. Moreover, it requires a cell voltage of 1.46 V to approach 50 mA cm-2, about 250 mV less than that of water electrolysis, confirming the less energy consumption. Notably, the N doped carbon protects Ni0.85Se/NiSe2 nanocrystals from aggregation leading to a faster CO2 desorption from Ni sites, which endow the Ni0.85Se/NiSe2@NC-2 a much better working stability. The direct urea hydrogen peroxide fuel cell (DUHPFC) achieves a maximum power density of 9.09 mW cm-2 at 20 °C. This work extends highly efficient dual-phased structure loading in NC catalysts system for urea-assisted energy conversion.

Phase and crystallinity regulations of Ni(OH)2 by vanadium doping boost electrocatalytic urea oxidation reaction.

Direct urea fuel cell (DUFC) and overall urea splitting system have attracted considerable attention as promising choice for energy conversion. Whereas, the anodic half reaction of electrocatalytic urea oxidation reaction (UOR) in these systems awfully limited their practical application due to the complex 6-electron transfer process. Herein, vanadium doped nickel (V-Ni(OH)2) with highly efficient electrocatalytic activity toward UOR was developed by a simple coprecipitation method. The introducing of V not only promotes the phase transforming from inactive ß-Ni(OH)2 to highly active α-Ni(OH)2, but also simultaneously modulates the electron environment of Ni, facilitating high valence species Ni3+ generation in low overpotential, enhancing the electrocatalytic activity potent of each Ni3+ site and speeding up the electrocatalytic reaction. The optimal V-Ni(OH)2 catalyst exhibits a summit current density of 241 mA cm-2 at 1.6 V vs. RHE, a Tafel slope of 32.15 mV dec-1, outperforming ß-Ni(OH)2 and most catalysts that tested on glassy carbon electrode. Furthermore, the assembled direct urea hydrogen peroxide fuel cell (DUPFC) offers a maximum power density of 13.4 mW cm-2 at 20 °C. This work provides an example of combing phase-regulation and electron modulation method for effective UOR electrocatalysts design.

F-decoration-induced partially amorphization of nickel iron layered double hydroxides for high efficiency urea oxidation reaction.

The urea oxidation reaction (UOR) has been well-acknowledged as one of the promising alternatives for hydrogen production through electrochemical water splitting system because of the more favorable thermodynamic potential. But the shortage of cost-effective electrocatalysts with high catalytic activity and durability restricts its practical development. Herein, the partially amorphous fluorine-decorated nickel iron layered double hydroxides (NiFe-F) is constructed via a low-temperature fluoridation method. Our study found that HF acid etching of NiFe LDH precursor resulted in the partially amorphous feature and abundant oxygen vacancies, providing rich reaction sites. Simultaneously, the formation of ionic metal-F bond makes it easier to form high-valence metal oxygen hydroxide active sites. Specifically, the as-prepared NiFe-F-4 electrode demonstrates a superb mass activity of 1290 mA mg-1 at 1.6 V vs. RHE. Further experiments found that amorphous structure and F decorating decreased the activation energy of UOR from 30.71 kJ mol-1 (crystalline NiFe-F-4) to 20.17 kJ mol-1 (amorphous NiFe-F-4), leading to a rapid dynamic with a small Tafel slope of 31 mV dec-1. Moreover, NiFe-F-4 casts remarkable long-term durability for 40 h without performance decay. This work holds great promise to develop advanced electrocatalysts for pollution treatment of urea-rich wastewater and energy-saving H2 production.

Superhydrophilic nickel cyclotetraphosphate for the hydrogen evolution reaction in acidic solution.

Nickel cyclotetraphosphate grown on carbon cloth (Ni2P4O12/CC) is synthesized via an anion exchange reaction method and it shows excellent hydrogen evolution reaction (HER) activity and strong working stability in acid due to the merits of its unique polymer-like structure, mesoporous characteristics, and superhydrophilic surface.