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The large-scale application of oxygen evolution reaction electrocatalysts is limited by many challenges such as sluggish kinetics, low conductivity, and instability. Remarkably, Co 3+ plays a vital role in oxygen evolution catalytic process because Co 3+ ions are regarded as active sites. Developing catalysts with high Co 3+ content is highly promising to improve the efficiency of water oxidation. In this study, we report a novel design method through controlling pH value and potential guided by Pourbaix diagram to synthesize surface Co 3+ -rich catalyst. The as-prepared catalyst possesses enhanced electrode-electrolyte contact area and lower diffusion resistance. In alkaline media, this catalyst exhibits promising oxygen evolution performance, with lower onset overpotential, satisfactory overpotential, and high value of turnover frequency (TOF). [ABSTRACT FROM AUTHOR]

Currently, developing highly active and low-cost electrocatalytic materials for oxygen evolution reaction (OER) is an enormously grand challenge. Herein, we developed a novel and highly active Mn doped Co 2 Fe layer double hydroxide (LDH) electrocatalyst for OER. We discovered that these electrocatalytic materials can be directly grown on carbon papers to construct high-specific-surface-area electrode, which shows the lowest overpotential of 266 mV at 10 mA cm−2. Furthermore, after introducing Mn element, DFT + U calculation found that the ∗OOH of Fe-site on Co 2 Fe 0.67 Mn 0.33 LDH could draw more electrons than Co 2 Fe LDH due to the electronegativity differences between Fe-site on Co 2 Fe 0.67 Mn 0.33 LDH and Fe-site on Co 2 Fe LDH, which is reason that the energy level of Fe 3d (e g) was obviously downshifted by d-d repulsion of Mn 3d and Fe 3d in the neighboring sites of Co 2 Fe 0.67 Mn 0.33 LDH after doped Mn element, which leads to reduce charge-transfer energy from O 2p to Fe 3d (e g) to promote oxygen evolution processes for OER. Meanwhile, the band gap is also decreased after doped Mn element in Co 2 Fe LDH due to the downshifted e g orbital energy of Fe 3d. This study gives a general avenue to design and developing efficiently active LDH electrocatalysts for OER in the future. • Both bimetallic CoFe LDH and Mn doped CoFe LDHs directly grown on carbon paper are successfully synthesized. • The Co 2 Fe 0.67 Mn 0.33 LDH@NFs exhibits a small overpotential of 236 mV at 10 mA cm−1 for OER. • DFT + U studies reveal that the observed superb OER activity could be attributed to d-d repulsion of Mn 3d and Fe 3d. [ABSTRACT FROM AUTHOR]

[Display omitted] • CoM x O y /Co 3 O 4 nanoarrays are synthesized via an in-situ self-templating strategy. • The electrocatalysts exhibit excellent OER activities in alkaline electrolyte. • Co atoms go through a dissolution-redeposition process during long-term stability test. • Partially dissolved cobalt ions adjacent to the surface precipitate into Co(OH) 2. Developing highly active and steady electrocatalysts for oxygen evolution reaction (OER) is crucial to achieve efficient electrochemical water splitting. Herein, we report a facile in situ self-assembly strategy for the synthesis of catalysts (CoMoO 4 /Co 3 O 4 /NF, CoWO 4 /Co 3 O 4 /NF and Co 3 V 2 O 8 /Co 3 O 4 /NF) with hierarchical 1D nanostructure. This 1D well-aligned structure and phase interpenetration of mixed Co species provide a rapid channel for charge transfer and mass exchange. Meanwhile, the internal Co 3 O 4 nanowires serve as a framework to host abundant CoM x O y (M = Mo, W, V) materials and this structure is beneficial to the exposure of OER active phases. As a result, these electrocatalysts exhibit excellent OER activities with low overpotentials. Besides, after 1000 voltammetry cycles, only slight increase in the overpotential verifies the excellent stability of these catalysts during the alkaline oxygen evolution reaction process. Based on postmortem characterizations, a dissolution–redeposition process is proposed to explain the formation of Co(oxy)hydroxides on the surface of the catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cu-Al 2 O 3 -CRB catalyst with DRCs is highly effective for destructing Ni-EDTA. • Biochar improved Cu species loading and electron polarization distribution. • The presence of CaCO 3 further promoted the formation of electron-rich Cu regions. • Decomplexation mechanism of Ni-EDTA over Cu-Al 2 O 3 -CRB catalyst was proposed. In this study, a calcium-rich biochar (CRB)-enhanced dual reaction center (DRC) Fenton-like catalyst, Cu-Al 2 O 3 -CRB, was synthesized for the decomplexation of a typical heavy metal complex pollutant, Ni-ethylenediaminetetraacetic acid (Ni-EDTA), in industrial wastewater. After a 90-minute reaction, the removal rate of Ni(II) could reach 95.2%, regardless of the initial solution pH. Various characterization analyses confirmed the formation of electron-rich Cu regions and electron-deficient Al and C regions in the Cu-Al 2 O 3 -CRB catalyst. The catalytic oxidation experiments, chronoamperometry tests, and reactive oxygen species (ROSs) detection further revealed the roles of biochar and CaCO 3 on the catalytic behavior of Cu-Al 2 O 3 -CRB catalyst. The presence of biochar not only enhanced the loading of Cu species but also introduced additional electron transfer channels, while CaCO 3 further interacted with biochar/Cu species to amplify the electron cloud density surrounding Cu. The improvement of electronic polarization facilitated the activation of H 2 O 2 and the generation of •O 2 –, 1O 2 and •OH. Contrary to conventional interfacial reactions, the weak adsorption between Cu-Al 2 O 3 -CRB and Ni-EDTA due to the electrostatic repulsion, led to the decomplexation reactions primarily occurring in the solution phase, rather than on the catalyst surface. This study sheds light on the potential of Cu-Al 2 O 3 -CRB as a DRC catalyst and emphasizes the significance of contaminant properties when using this kind of catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Multiple techniques reveal LaNiO 3 surface reconstruction central to oxygen evolution reaction. • OER activity notably influenced by soluble Fe species in electrolyte, a common impurity. • Increasing OER activity is coupled to redox active Ni amount from peak integration. • La 2 NiO 4 intrinsically more prone to redox active Ni formation than LaNiO 3. The accurate description of activity trends among perovskite-oxide oxygen-evolution-reaction (OER) catalysts using electronic-structure descriptors requires that the bulk structure of the catalyst is comparable to that of the surface. Few studies have addressed the dynamic nature of the catalyst's structure during the OER and the consequential implications for understanding activity. Here, we use a combination of electrochemical and materials-characterization techniques to study the surface reconstruction and the associated formation of a new redox-active phase on LaNiO 3 particles, LaNiO 3 epitaxial films, and an analogous Ruddlesden-Popper phase, La 2 NiO 4. Small, but characteristic, redox features corresponding to Ni redox in nominally amorphous NiO x H y are observed during cyclic voltammetry of these initially fully crystalline materials. The size of these redox features grows with prolonged cycling and contributes to an increased surface area as determined from electrochemical impedance spectroscopy (EIS). We find the OER activity is strongly dependent on soluble Fe species in the electrolyte, common impurities in alkaline media. These observations are consistent with the reconstruction of the crystalline surface to form NiO x H y species and subsequent activation by adsorption of Fe forming the well-known and extremely active NiFeO x H y OER catalyst. [ABSTRACT FROM AUTHOR]

Shape-controlled synthesis of non-noble metal nanocrystals (NCs) is vital to their catalysis applications due to their different exposed surfaces and atomic coordination environments. Here, we report a facile synthesis of Ni nanocubes and cuboctahedra with controlled shapes and high yields via a wet-chemistry strategy. The key to success relies on the use of cetyltrimethyl ammonium bromide (CTAB), formaldehyde (HCHO) and a specific reaction temperature, which could effectively cap the desired surface and tune their growth rate. Specifically, nanocubes switched to cuboctahedra and octahedra with an increased reaction temperature due to gradual CO desorption from the surfaces of NCs. Meanwhile, it should be worth noting that CTAB and the generated CO molecules through HCHO decomposition would co-adsorb on the {100} facets of Ni NCs. As a proof-of-application, the obtained Ni NCs exhibited high activity in the oxygen evolution reaction (OER) with over-potentials of 383 mV and 402 mV for nanocubes and cuboctahedra at a current density of 10 mA cm−2, respectively, demonstrating that the {100} facets are more favorable toward OER. These results suggested that their performance is strongly shape dependent and is derived from different surface energies and active sites. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The ZIF-67-derived hollow CoS shows a high specific capacitance of 720 F g−1. • The anode and cathode of the capacitor are derived from the same precursor. • The surface capacitive contribution is dominated in hollow CoS energy storage. • Assembled capacitor shows a maximum energy density of 80 Wh kg−1. Abstract In this work, hollow CoS nanobox (noted as HCSN) have been successfully synthesized via annealing and hydrothermal process from zeolitic imidazolate framework (ZIF-67) template. When tested as positive electrode materials in alkaline aqueous electrolyte, it shows high specific capacitance of 720 F g−1 at a current density of 1 A g−1, good rate capability (82.1%) and good cycling stability with 86.4% capacitance retention over 10,000 cycles at 10 A g−1. To further demonstrate the advantages of our ZIF-67 derived materials, asymmetric energy storage device was assembled (HCSN//NC), where the as-prepared HCSN was employed as the anode and ZIF-67-derived nanoporous carbon (noted as NC) as the cathode. This device achieves high energy density (80 Wh kg−1 at a specific power density of 882 W kg−1), good rate capability (53.3 Wh kg−1 even at a specific power density of 7.9 kW kg−1) and long-term stability up to 10,000 cycles. More importantly, it could simultaneously light up 12 LEDs in parallel, demonstrating its potential in practical applications. [ABSTRACT FROM AUTHOR]