Self-supported electrodes comprising carbon fi ber paper (CP) integrated with bifunctional nickel phosphide (Ni-P) electrocatalysts are fabricated by electrodeposition of Ni on functionalized CP, followed by a convenient one-step phosphorization treatment in phosphorus vapor at 500 °C. The as-fabricated CP@Ni-P electrode exhibits excellent electrocatalytic performance toward hydrogen evolution in both acidic and alkaline solutions, with only small overpotentials of 162 and 250 mV, respectively, attaining a cathodic current density of 100 mA cm −2 . Furthermore, the CP@Ni-P electrode also exhibits superior catalytic performance toward oxygen evolution reaction (OER). An exceptionally high OER current of 50.4 mA cm −2 is achieved at an overpotential of 0.3 V in 1.0 M KOH. The electrode can sustain 10 mA cm −2 for 180 h with only negligible degradation, showing outstanding durability. Detailed microstructural and compositional studies reveal that upon OER in alkaline solution the surface Ni-P is transformed to NiO covered with a thin Ni(OH) x layer, forming a Ni-P/NiO/Ni(OH) x heterojunction, which presumably enhances the electrocatalytic performance for OER. Given the well-defi ned bifunctionality, a full alkaline electrolyzer is constructed using two identical CP@Ni-P electrodes as cathode and anode, respectively, which can realize overall water splitting with effi ciency as high as 91.0% at 10 mA cm −2 for 100 h.

A notable trend in OER activity on transition metal phosphide pre-catalysts is reported. Remarkably, the tri-metallic FeCoNiP pre-catalysts exhibit exceptional apparent and intrinsic OER activities, outperforming many non-precious OER catalysts reported previously.

Synergistic coupling of ruthenium with cobalt phosphide can significantly boost the hydrogen evolution performance of the hybrid catalysts in a wide pH range.

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Dynamic morphological, structural and compositional changes will occur when transition metal phosphides and chalcogenides are used to catalyze the oxygen evolution reaction, which can substantially enhance their electrocatalytic performance.

using electrocatalysts, the OER will take place at a high overpotential leading to significant losses of the overall efficiency of water splitting. Although RuO 2 and IrO 2 are highly efficient catalysts for the OER, [1b] the exorbitant price and scarcity of Ru and Ir severely restrict their widespread use in electrolyzers.Remarkable progress has been made in developing efficient nonprecious OER electrocatalysts, such as perovskite oxides, [3] transition metal (TM) oxides, [4] (oxy)hydroxides, [5] phosphates, [6] phosphides, [7] nitrides, [8] chalcogenides, [9] and metal-free carbon nanostructures. [10] Recently, cobalt selenide with different polymorphs has attracted considerable attention for use as efficient catalysts to expedite the OER in basic solution [9a-f ] or the HER in acidic solution, [11] most of which were prepared by a two-step method involving either the synthesis of Co-containing precursors followed by a selenization process, [11a-f ] or the synthesis of selenide precursors followed by a cation-exchange process. [9f ] Since the high OER activity expected for pure cobalt selenide remains out of reach, strategies that can enhance the OER activity of cobalt selenide have been explored. For example, composites of CoSe 2 with graphene [9d] or metal oxides [9a,e] were reported, and exhibited OER activity substantially higher than that of pure CoSe 2 . The enhanced OER activity is believed to result from the synergistic interaction between cobalt selenide and graphene/ metal oxides. [9a,d,e] Besides, ultrathin CoSe 2 nanosheets (NSs) and atomic layers were synthesized by delaminating lamellar hybrid CoSe 2 -DETA (DETA = diethylenetriamine) intermediates, with the aim of exposing more low-coordinated catalytically active sites and achieving better structural stability. [9b,c] These NSs and single-unit-cell atomic layers have accomplished substantially improved OER activity compared to both bulk CoSe 2 and CoSe 2 -DETA intermediates, requiring only a low overpotential (η) of 320 mV at 10 mA cm −2 in basic medium and showing a small Tafel slope of 44 mV decade −1 (dec −1 ). [9b] While CoSe 2 is still the most commonly studied polymorph of cobalt selenide, [9a−f,11] nonstoichiometric cobalt selenide (e.g., Co 0.85 Se) has drawn great attention very recently Cobalt selenide has been proposed to be an effective low-cost electrocatalyst toward the oxygen evolution reaction (OER) due to its well-suited electronic configuration. However, pure cobalt selenide has by far still exhibited catalytic activity far below what is expected. Herein, this paper for the first time reports the synthesis of new monoclinic Co 3 Se 4 thin nanowires on cobalt foam (CF) via a facile one-pot hydrothermal process using selenourea. When used to catalyze the OER in basic solution, the conditioned monolithic selfsupported Co 3 Se 4 /CF electrode shows an exceptionally high catalytic current of 397 mA cm −2 at a low overpotential (η) of 320 mV, a small Tafel slope of 44 mV dec −1 , a turnover frequency of 6.44 × 10 −2 ...

Construction of heterojunctions has aroused great interest recently in the photocatalysis field because of the special electronic band structure and unique physicochemical properties. In this work, a novel 0D/3D CuO/ZnO heterojunction was obtained via in situ deposition of CuO nanoparticles on the flowerlike ZnO surface using the wet chemistry method. After depositing CuO nanoparticles onto the ZnO, the CuO/ZnO heterojunction exhibits enhanced visible-light harvesting and effective separation of the photogenerated electron–hole pairs compared with those in the pure ZnO. The photocatalytic removal efficiency of phenol over the CuO/ZnO heterojunction is up to 78% under the irradiation of the light, which is ∼2 and ∼4 times higher than those of the pristine ZnO and CuO, respectively. This composite also presents good durability and stability for phenol degradation in the photocatalytic reactions. Additionally, in the photodegradation system of the CuO/ZnO heterojunction, the superoxide radicals (•O2 –) and hydroxyl radicals (•OH) are confirmed as the active species by the trapping experiments. This research provides a promising way to achieve 0D/3D heterojunctions for the application in environmental purification and remedy.

Self-supported porous Ni–P foam is fabricated by a convenient one-step method, and exhibits excellent electrocatalytic performance towards oxygen evolution reaction. An alkaline electrolyzer constructed using two self-supported porous Ni–P foams shows superior energy efficiency of 90.2% at 10 mA cm−2, and can sustain 1000 h under operation conditions without obvious degradation.