One of the challenges to realize large-scale water splitting is the lackofactive and low-cost electrocatalysts for its two half reactions:H 2 and O 2 evolution reactions (HER and OER). Herein, we report that cobalt-phosphorous-derived films (Co-P) can act as bifunctional catalysts for overall water splitting.T he as-prepared Co-P films exhibited remarkable catalytic performance for both HER and OER in alkaline media, with ac urrent density of 10 mA cm À2 at overpotentials of À94 mV for HER and 345 mV for OER and Tafel slopes of 42 and 47 mV/dec, respectively.T hey can be employed as catalysts on both anode and cathode for overall water splitting with 100 %F aradaic efficiency,rivalling the integrated performance of Pt and IrO 2 .T he major composition of the asprepared and post-HER films are metallic cobalt and cobalt phosphide,w hichp artially evolved to cobalt oxide during OER.

The development of high-performance nonprecious electrocatalysts with both H2 and O2 evolution reaction (HER and OER) activities for overall water splitting is highly desirable but remains a grand challenge. Herein, we report a facile two-step method to synthesize three-dimensional hierarchically porous urchin-like Ni2P microsphere superstructures anchored on nickel foam (Ni2P/Ni/NF) as bifunctional electrocatalysts for overall water splitting. The Ni2P/Ni/NF catalysts were prepared by template-free electrodeposition of porous nickel microspheres on nickel foam followed by phosphidation. The hierarchically macroporous superstructures with 3D configuration can reduce ion transport resistance and facilitate the diffusion of gaseous products (H2 and O2). The optimal Ni2P/Ni/NF exhibited remarkable catalytic performance and outstanding stability for both the HER and OER in alkaline electrolyte (1.0 M KOH). For the HER, Ni2P/Ni/NF afforded a current density of 10 mA cm–2 at a low overpotential of only −98 mV. When it served as an OER electrocatalyst, Ni2P/Ni/NF was partially oxidized to nickel oxides/hydroxides/oxyhydroxides (mainly NiO) on the catalyst surface and exhibited excellent OER activity with small overpotentials of 200 and 268 mV to reach 10 and 100 mA cm–2, respectively. Furthermore, when Ni2P/Ni/NF was employed as the electrocatalyst for both the cathode and anode, a water splitting electrolyzer was able to reach 10 and 100 mA cm–2 in 1.0 M KOH at cell voltages of 1.49 and 1.68 V, respectively, together with robust durability. Various characterization techniques and controlled experiments indicated that the superior activity and strong stability of Ni2P/Ni/NF for overall water splitting originated from its electrochemically active constituents, 3D interconnected porosity, and high conductivity.

The design of active, robust, and nonprecious electrocatalysts with both H 2 and O 2 evolution reaction (HER and OER) activities for overall water splitting is highly desirable but remains a grand challenge. Herein, we report a facile two-step method to synthesize porous Co-P/NC nanopolyhedrons composed of CoP x (a mixture of CoP and Co 2 P) nanoparticles embedded in N-doped carbon matrices as electrocatalysts for overall water splitting. The Co-P/NC catalysts were prepared by direct carbonization of Cobased zeolitic imidazolate framework (ZIF-67) followed by phosphidation. Benefiting from the large specific surface area, controllable pore texture, and high nitrogen content of ZIF (a subclass of metal−organic frameworks), the optimal Co-P/NC showed high specific surface area of 183 m 2 g −1 and large mesopores, and exhibited remarkable catalytic performance for both HER and OER in 1.0 M KOH, affording a current density of 10 mA cm −2 at low overpotentials of −154 mV for HER and 319 mV for OER, respectively. Furthermore, a Co-P/NC-based alkaline electrolyzer approached 165 mA cm −2 at 2.0 V, superior to that of Pt/IrO 2 couple, along with strong stability. Various characterization techniques including X-ray absorption spectroscopy (XAS) revealed that the superior activity and strong stability of Co-P/NC originated from its 3D interconnected mesoporosity with high specific surface area, high conductivity, and synergistic effect of CoP x encapsulated within N-doped carbon matrices.

The development of low-cost catalysts with oxygen reduction reaction (ORR) activity superior to that of Pt for fuel cells is highly desirable but remains challenging. Herein, we report a bimetalorganic framework (bi-MOF) self-adjusted synthesis of support-free porous Co-N-C nanopolyhedron electrocatalysts by pyrolysis of Zn/Co bi-MOF without any post-treatments. The presence of initial Zn forms a spatial isolation of Co which suppresses its sintering during pyrolysis and the Zn evaporation also promotes the surface area of the resultant catalysts. The composition, morphology, and hence ORR activity of Co-N-C could be tuned by the Zn/Co ratio. The optimal Co-N-C exhibited remarkable ORR activity with a half-wave potential of 0.871 V vs RHE (30 mV more positive than that of commercial 20 wt% Pt/C) and a kinetic current density of 39.3 mA cm -2 at 0.80 V vs RHE (3.1 times that of Pt/C) in 0.1 M KOH, plus excellent stability and methanol tolerance. It also demonstrated comparable ORR activity and much higher stability than those of Pt/C in acidic and neutral electrolytes. Various characterization techniques including X-ray absorption spectroscopy revealed that the superior activity and strong stability of Co-N-C originated from the intense

Electrocatalytic water splitting to produce H2 plays an important role in the capture, conversion, and storage of renewable energy sources, such as solar energy and wind power.