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The preparation of noble metal‐free catalysts for water splitting is the key to low‐cost, sustainable hydrogen generation. Herein, through a pyrolysis‐oxidation process, we prepared a series of Co‐Fe‐Ni trimetallic oxidized carbon nanocubes (Co1‐XFeXNi‐OCNC) with a continuously changeable Co/Fe ratio (X=0, 0.1, 0.2, 0.5, 0.8, 0.9, 1). The Co1‐XFeXNi‐OCNC shows a volcano‐type oxygen evolution reaction (OER) activity. The optimized Co0.1Fe0.9Ni‐OCNC achieves a low overpotential of 268 mV at 10 mA cm−2 with a very low Tafel slope of 48 mV dec−1 in 1 m KOH. At the same time, the stability of the Co0.1Fe0.9Ni‐OCNC is also outstanding; after 1000 CV cycles, the LSV plot is almost coincident. Moreover, the potential remains almost of the same value at 10 mA cm−2 after 12 h in comparison to the initial value. The excellent electrocatalytic properties can be attributed to the synergistic cooperation between each component. Therefore, the Co0.1Fe0.9Ni‐OCNC is a promising candidate instead of precious metal‐based electrocatalysts for OER. [ABSTRACT FROM AUTHOR]

Currently, the design and application of low‐cost and highly active bifunctional electrocatalysts for oxygen evolution reactions (OERs) and hydrogen evolution reactions (HERs) are still challenging. Metal‐organic frameworks (MOFs) are used to produce a material composed of porous nitrogen‐doped carbon materials encapsulating cobalt and tungsten carbide (Co/W‐C@NCNSs). Nanoscale MOFs are successfully synthesized via a microwave method and are denoted as HZIF‐W. Moreover, the obtained MOFs are annealed under N2 atmosphere at a temperature of 600 and 800 °C, and the obtained samples are designated as Co/W‐C@NCNSs(600) and Co/W‐C@NCNSs(800), respectively, according to the annealing temperature. The results show that the obtained Co/W‐C@NCNSs exhibit superior performance toward both the OER and HER in alkaline media. Co/W‐C@NCNSs(800) shows the best electrocatalytic activities, requiring an overpotential of 323 mV (vs RHE) and −252 mV (vs RHE) to achieve a current density of 10 mA cm−2 for the electrocatalytic OER and HER in an aqueous solution. A water electrolyzer device using Co/W‐C@NCNSs(800) as both the anode and cathode requires only a cell voltage of 1.68 V to reach a current density of 10 mA cm−2, thus illustrating that cobalt/tungsten carbide‐based NCNSs derived from MOFs can be prospective materials for the electrocatalysis of water splitting. [ABSTRACT FROM AUTHOR]

Abstract Metal-organic frameworks (MOFs) benefitting from its controllable and diverse structure are a class of promising materials for diverse field. However, its directly employed for oxygen evolution reaction (OER) is still rare. Particularly, two-dimensional (2D) MOF nanosheets materials possess both advantages of 2D layered nanomaterials and MOFs, are considered as promising nanomaterials. Herein, we report a facile and scalable in situ hydrothermal synthesis of a 2D Co-based bimetallic MOFs (Co-Fe/Ni@HPA-MOF nanosheets), which can be stable in alkaline solution and directly adopted as highly efficient electrocatalysts. The Co-Ni@HPA-MOF can reach a current density of 10 mA cm−2 at low overpotential of 320 mV with a small Tafel slope of 58 mV dec−1, which is comparable to that of commercial RuO 2 (58 mV dec−1). The excellent electrocatalytic properties can be attributed to the 2D nanosheet and the coupling effect between Co and Ni, which provided large number of accessible active sites. The results highlight the great potential of utilizing MOF nanosheets for electrocatalysis, and will pave a way to develop more efficient 2D MOFs for diverse catalytic applications. Graphical abstract A facile and scalable in situ hydrothermal synthesis of a two dimensional Co-based bimetallic MOFs (Co-Fe/Ni@HPA-MOF nanosheets) was reported, which can be stable in alkaline solution and directly adopted as highly efficient electrocatalysts. fx1 Highlights • Two dimensional (2D) Co-based bimetallic metal-organic frameworks (MOFs) nanosheets were fabricated. • The Co-Ni@HPA-MOF nanosheet can reach a current density of 10 mA cm−2 at low overpotential of 320 mV. • The excellent electrocatalytic properties can be attributed to the coupling effect between Co and Ni. [ABSTRACT FROM AUTHOR]

Nowadays, there still exists big challenges to synthesize active and inexpensive electrocatalysts for oxygen evolution reaction. In this work, we propose a new method by using melamine‐uric acid (MAUA) supramolecular nanofibers as precursor to fabricate metal‐embedded nitrogen‐doped carbon nanotube materials (MM′@NCNTs, M, M′ = Fe, Co, Ni). The samples exhibit superior and stable catalytic performance for oxygen evolution reaction (OER) in alkaline medium. In all the electrocatalysts, FeNi@NCNT shows the best electrocatalytic activity with the overpotential is only 402 mV (vs. RHE) at 10 mA·cm–2, which shows better performance than both Fe@NCNT and Ni@NCNT. The smaller Tafel slope value, with the value of 68 mV·dec–1, indicates the superior OER activity of FeNi@NCNT. These results reveal a synergistic effect between Fe, Co, and Ni, which could produce a favorable coordination environment that enhance the activity for oxygen evolution reaction. [ABSTRACT FROM AUTHOR]

A facile method is reported to form a honeycomb‐like porous nanomaterial by intercalation of iron nitrate using nature silk sericin (SS) as nitrogen and carbon source. A series of Fe2O3 nanoparticles anchored on Fe2O3‐N‐doped graphite carbon electrocatalysts (SS‐Fe) were synthesized, exhibits well‐defined pore structure and excellent oxygen evolution reaction (OER) catalytic activities. Among these materials, SS‐Fe‐0.5 shows the best performance, the overpotential of SS‐Fe‐0.5 at 10 mA·cm–2 is 440 mV (vs. RHE) and the Tafel slope is only 68 mV·dec–1. The results indicate that it is promising to the preparation of carbon catalyst materials using natural, renewable and abundant resources for electrocatalysis. [ABSTRACT FROM AUTHOR]

In this paper, we reported the fabrication of Co-embedded nitrogen-doped carbon nanotube (Co-NCNT) by using Co-melamine coordination polymer (CP) as precursor. The sample was well characterized via SEM, TEM, XRD, XPS and BET methods. The Co-NCNT shows excellent and stable catalytic performance for OER. The overpotential of Co-NCNT at 10 mA cm -2 is 370 mV (vs RHE). The current density of Co-NCNT could reach 100 mA cm -2 at overpotential of 520 mV, which showed much better performance than RuO 2 , while the largest current density of RuO 2 could reach is only 44 mA cm -2 . The Tafel slope of Co-NCNT is 56 mV dec -1 , which is smaller than that of commercial RuO 2 (58 mV dec -1 ). The results indicate that metal-melamine based CPs or MOFs can be promising precursors for the preparation of efficient metal-embedded nitrogen-doped carbon materials for electrocatalysis. [ABSTRACT FROM AUTHOR]