Bimetallic Ni–Mo nitride nanotubes as highly active and stable bifunctional catalysts for full water splitting are favorably comparable to the performance of Pt/C and IrO2.

hydrogen fuel. To achieve high energy storage and conversion efficiencies, highperformance electrocatalysts are required. Precious metals such as Pt have shown high activity toward the hydrogen evolution reaction (HER) and the oxygen reduction reaction (ORR), while RuO 2 and IrO 2 have shown excellent activity toward the oxygen evolution reaction (OER). [1,2] Nevertheless, their high cost and low natural abundance have significantly limited the large-scale utilization of those precious electrocatalysts. Therefore, many efforts have been made to explore the nonprecious metal based electrocatalysts for full water splitting and metal-air batteries. Furthermore, to further reduce the cost for energy storage and conversion devices, it is highly desirable to develop trifunctional electrocatalysts that can catalyze the HER, ORR, and OER simultaneously in the same electrolyte.Recently, nonprecious transition-metal compound nanostructures with various morphologies have been reported for catalyzing the HER, OER, and/or ORR. Among these electrocatalysts, the nanotube (NT)-based ones with open ends and/ or porous features have attracted much interest because of their hollow interiors, porous characteristics, and large surface area, which greatly facilitate the exposure of active sites to the electrolyte, the quick diffusion of electrolyte into the active species, and the quick release of the thus-formed hydrogen and oxygen bubbles from the catalyst surface. Typically, tubular nanostructures, including Mo 2 C, [3,4] MoS 2 , [5,6] MoSe 2 , [7] Ni-Mo nitride, [8] Ni-Co selenide, [9] Ni-Co hydroxide, [10] Ni-Co nitride, [11] MoS 2 /SnO 2 , [12] and MoO x /MoS 2 [13] for catalyzing the HER, FeOOH/CeO 2 , [14] FeOOH/Co/FeOOH, [15] CoO x , [16] and Ni-Co phosphide [17] for catalyzing the OER, and Pt-Co/CN x , [18] PtAuCu, [19] Co@Co 3 O 4 /carbon nanotubes (CNTs), [20] CoSe 2 / CNTs, [21] NiCo/CNTs, [22] and Co x Mn 3−x O 4 , [23] for catalyzing the OER and ORR have been reported. Despite the advances in the transition-metal nanotube electrocatalysts for the HER, OER, and ORR, high-performance trifunctional electrocatalysts based on transition-metal nanotubes that can catalyze the HER, OER, and ORR simultaneously in the same electrolyte have rarely been reported.Besides controlling the morphology, tuning the electronic structure of the electrocatalysts through introducing heteroatoms into the catalyst host or designing multimetal catalysts has been considered as an important and efficient method for increasing the activities of electrocatalysts. [24][25][26][27][28][29] Among the multimetal catalysts mentioned above, Ni-Fe bimetal-based High-performance catalysts are required in various energy storage and conversion systems. In this work, hierarchical Ni-Fe-Mo trimetal nitride nanotubes (NTs) as highly efficient, low-cost, robustly stable, multifunctional catalysts through room-temperature Fe incorporation and subsequent thermal treatment for full water splitting and Zn-air batteries are fabricated. The two-electrode electrolyzer ...

To improve the efficiency of overall water splitting, highly active and stable bifunctional electrocatalysts are highly desirable. Herein, we fabricated mixed Ni-Co phosphides (NiCo-P) as bifunctional catalysts for overall water splitting. Structural characterizations indicated that the NiCo-P catalysts (0 > x > 1) exhibited hierarchical yolk-shelled morphologies, with a total diameter of 1-2 μm. Interestingly, the shell was assembled by numerous nanosheets with a thickness less than 10 nm. The electrochemical measurements indicated that the NiCo-P catalysts (0 < x < 1) showed significantly enhanced OER and HER activities in comparison to the pure Ni-P and Co-P catalysts, and the highest OER and HER activities were achieved as x = 0.31. To drive a current density of 10 mA cm, the NiCo-P catalyst required an overpotential of 266 mV for OER and 96 mV for HER, respectively. The alkaline water electrolyzer with the NiCo-P catalysts as the cathode and anode catalysts required a cell voltage of ca. 1.59 V to achieve a current density of 10 mA cm, which was comparable to the integrated performance of commercial Pt/C and IrO. Furthermore, the electrolyzer assembled by the bufictional electrocatalysts showed a more stable performance than one assembled by commercial Pt/C and IrO operated at the simialr current density. The superior activity and long-term stability demonstrate that the hierarchical mixed Ni-Co phosphides have promising potential for application in large-scale water splitting.