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Graphical abstract Highlights • The uniform bimetallic CoFeP hollow microspheres have been synthesized. • The hollow structure of CoFeP is helpful to increase the exposed actives. • The bimetallic composites can provide the better intrinsic activity. • The synergistic effect from bimetallic phosphides contributes to the enhanced performances. Abstract The ingenious design and synthesis of bifunctional electrocatalysts with high activity and robust stability for hydrogen evolution reaction and oxygen evolution reaction (HER and OER) is desirable and challenging. Herein, bimetallic phosphides CoFeP with hollow microspheres structure has been synthesized through a facile gas phosphorization as bifunctional electrocatalyst for overall water splitting. SEM and TEM demonstrate the formation of uniform hollow microspheres of CoFeP. The hollow structure of CoFeP is helpful to increase the exposed actives and the larger contact surface with electrolyte. The bimetallic composites can provide the better intrinsic activity. Compared with single metallic phosphides CoP and FeP, the obvious enhancement of electrocatalytic performances of CoFeP can be observed. The electrochemical results show that the bimetallic CoFeP hollow microspheres only have the lower overpotential of 177 and 350 mV (vs. RHE) to drive a current density of 10 mA cm−2 for HER and OER, respectively. The reasons may be due to the hollow nanostructure and the synergistic effect from bimetallic phosphides. This work provides a facile and effective way to design excellent phosphides electrocatalysts for water splitting based on gas phosphorization of bimetallic oxides precursors. [ABSTRACT FROM AUTHOR]

It is impending but still a big challenge to design and synthesize electrocatalyst with typical nanostructure and efficient catalytic activity for hydrogen evolution reaction (HER). Herein, we report a low-temperature phosphorization process to synthesize nickel-iron bimetallic phosphides (NiFeP) using MIL-88-Fe 2 Ni MOF (metal-organic framework) as precursor. The as-synthesized NiFeP shows superior electrocatalytic performance with lower onset overpotential, smaller Tafel slope, bigger exchange current density and lower overpotential to reach the current density of 10 mA cm −2 than both NiP 2 and FeP for HER in alkaline solution. The enhanced electrochemical activity may be attributed to the existence of the synergistic effect between NiP 2 and FeP. SEM and TEM images show that the obtained NiFeP bimetallic phosphides preserve the size and morphology of the parent MIL-88-Fe 2 Ni MOF. And the prominent and stable performance of NiFeP nanorods for HER may also ascribes to the typical rod-like nanostructure with large specific surface area. [ABSTRACT FROM AUTHOR]

• The RuP 4 @CoP/Ti electrocatalyst with acacia-like structure was obtained using a facile method. • The incorporation of Ru can accelerate the charge transfer between Ru, Co, and P. • The RuP 4 @CoP/Ti possesses super activity under either acidic or alkaline solution. • The existence of Ti foil could enhance the electrical conductivity and disperse the active phases. The transition metal phosphate with lower price and rich abundance have a tendency to replace Pt-based catalytic materials for hydrogen evolution reaction (HER). Nevertheless, for transition metal phosphate based electrocatalyst, the further improvement of the electrocatalytic performance and the deep exploration of the regulation and control mechanism are still bottleneck problems. At present, we use a novel method to prepare the Ti foil supported the CoP acacia-like arrays decorated with RuP 4 nanoparticles composite (RuP 4 @CoP/Ti). The obtained RuP 4 @CoP/Ti possesses excellent electrocatalytic performance, which needs the overpotential of 66.2 mV to reach the current of density of 10 mA cm−2 and has the Tafel slope of 52.6 mV dec−1 in 0.5 M H 2 SO 4. In addition, it requires the overpotential of 36 mV to reach the current of density of 10 mA cm−2 and has Tafel slope of 54.8 mV dec−1 in 1 M KOH. Moreover, the obtained RuP 4 @CoP/Ti also presents outstanding long-term durability under either acidic or alkaline condition. The reason for such excellent properties is due to the unique acacia-like structure, the synergistic effect between CoP and RuP 4 , the existence of Ti foil and the introduction of Ru, which can optimize the electronic structure of Co and P. [ABSTRACT FROM AUTHOR]