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Abstract
Recent experimental findings suggest that the catalytic activity of Co3O4 for oxygen evolution reaction (OER) could be improved by nitrogen doping. We present preliminary OER modelling on a N-doped Co3O4 surface, with varying concentration of the dopant and its spatial distribution around Cooct and Cotet adsorption sites. The overpotential was calculated for two adsorption sites on seven types of N-doped Co3O4 surface. The largest calculated overpotential value for a N-doped surface was ~1V.

The project AP05131211 "First principles investigation on catalytic properties of N-doped Co3O4." was funded by the Ministry of Education and Science of the Republic of Kazakhstan. The work was partly supported by COST (European Cooperation in science and Technology) Action 18234 (YM and EK). The work of T. Inerbaev was performed under the state assignment of Sobolev Institute of Geology and Mineralogy Siberian Branch of the Russian Academy of Sciences. YM and EK thank Sun-to-Chem project of ERA Net. ; Recent experimental findings suggest that the catalytic activity of Co3O4 for oxygen evolution reaction (OER) could be improved by nitrogen doping. We present preliminary OER modelling on a N-doped Co3O4 surface, with varying concentration of the dopant and its spatial distribution around Cooct and Cotet adsorption sites. The overpotential was calculated for two adsorption sites on seven types of N-doped Co3O4 surface. The largest calculated overpotential value for a N-doped surface was ~1V. This work is licensed under a CC BY 4.0 license. ; Ministry of Education and Science of the Republic of Kazakhstan, project AP0513121; COST Action 18234; Sobolev Institute of Geology and Mineralogy Siberian Branch of the Russian Academy of Sciences; Sun-to-Chem project of ERA Net; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union's Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART².

Rational design of highly active electrocatalysts for the oxygen evolution reaction (OER) is critical to improving overall electrochemical water splitting efficiency. This study suggests hollow CeO2@Co2N nanosheets synthesized using Co-ZIF-L as a precursor, followed by a hydrothermal reaction and a nitridation process as very attractive OER catalysts. The increased activity is supposed to be due to nitridation and strong electronic interaction between CeO2 and Co2N that contribute to the formation of active CoOOH phase. The synthesized CeO2@Co2N exhibits low overpotentials of 219 and 345 mV at OER current densities of 10 and 100 mA cm–2, respectively, as well as a long-term durability of 30 h at a comparatively high current density of 100 mA cm−2. ; This research was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) within the collaborative research center/ transregio 247 "Heterogeneous Oxidation Catalysis in the Liquid Phase" TRR 247 (388390466). The project received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement CasCat (833408)). J.Z. acknowledges the Chinese Scholarship Council for a Ph.D. fellowship. Open access funding enabled and organized by Projekt DEAL.

Co3O4 nanocubes are evaluated concerning their intrinsic electrocatalytic activity towards the oxygen evolution reaction (OER) by means of single-entity electrochemistry. Scanning electrochemical cell microscopy (SECCM) provides data on the electrocatalytic OER activity from several individual measurement areas covering one Co3O4 nanocube of a comparatively high number of individual particles with sufficient statistical reproducibility. Single-particle-on-nano-electrode measurements of Co3O4 nanocubes provide an accelerated stress test at highly alkaline conditions with current densities of up to 5.5 Acm-2, and allows to derive TOF values of up to 2.8 X104 s-1 at 1.92 V vs. RHE for surface Co atoms of a single cubic nanoparticle. Obtaining such high current densities combined with identical-location transmission electron microscopy allows monitoring the formation of an oxy(hydroxide) surface layer during electrocatalysis. Combining two independent single-entity electrochemistry techniques provides the basis for elucidating structure–activity relations of single electrocatalyst nanoparticles with well-defined surface structure. ; This research obtained funding from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) within the collaborative research centre/transregio 247 "Heterogeneous Oxidation Catalysis in the Liquid Phase" TRR 247 [388390466] (projects A2 and C3) as well as under Germany's Excellence Strategy-EXC 2033-390677874-RESOLV. This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement CasCat [833408]). The mechanical workshop team at the faculty of chemistry and biochemistry, Ruhr University Bochum, is acknowledged for the contribution in designing and building the nanoelectrode TEM holder. We acknowledge Prof. Patrick Unwin from the University of Warwick for providing the initial control software (WEC-SPM) for our SECCM experiments. Open Access funding enabled and organized by ...

Developing efficient, durable, and low cost catalysts based on earth-abundant elements for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is essential for renewable energy conversion and energy storage devices. We report herein a simple one-pot procedure for the synthesis of non-precious metals N-doped graphene composites employing urea as nitrogen source, and their application as bifunctional catalysts for both the ORR and OER in alkaline environment. In this study, the effects of the addition of Ti and Co on the structure and performance of the N-doped graphene composites are investigated. The incorporation of Ti leads to a composite with both anatase and rutile TiO2 crystalline phases as well as Ti3+ species stabilized upon hybridization with N-doped reduced graphene oxide. The ORR onset potential for the Ti-based composite is 0.85 V (vs. RHE) and the number of electrons transferred is 3.5, showing superior stability than Pt/C after accelerated potential cycling in alkaline solution. However, this composite shows low activity and stability for the OER. On the other hand, the composite consisting of metallic Co and Co3O4 nanocrystals grown on N-doped reduced graphene oxide exhibits the best performance as bifunctional catalyst, with ORR and OER onset potentials of 0.95 V and 1.51 V (vs. RHE), respectively, and a number of electrons transferred of 3.6 (ORR). The results reveal the presence of important structural features such as metallic Co as the predominant crystalline component, amorphous Co3O4 phase and the coordination of Co-N-doped graphene. All of them seem to be fundamental for the high activity and stability towards ORR and OER. ; Authors acknowledge financial support given by Spanish Ministry of Economy and Competitiveness (MINECO) through projects ENE2014-52158-C2-1-R and 2-R (co-founded by FEDER). J. M. Luque and G. Lemes also thank MINECO and Aragon Government, respectively, for their Ph.D. grants. ; Peer reviewed

The number of active sites and their intrinsic activity are key factors in designing high-performance catalysts for the oxygen evolution reaction (OER). The synthesis, properties, and in-depth characterization of a homogeneous CoNiFeCu catalyst are reported, demonstrating that multimetal synergistic effects improve the OER kinetics and the intrinsic activity. In situ carbon corrosion and Cu leaching during the OER lead to an enhanced electrochemically active surface area, providing favorable conditions for improved electronic interaction between the constituent metals. After activation, the catalyst exhibits excellent activity with a low overpotential of 291.5 ± 0.5 mV at 10 mA cm−2 and a Tafel slope of 43.9 mV dec−1. It shows superior stability compared to RuO2 in 1 m KOH, which is even preserved for 120 h at 500 mA cm−2 in 7 m KOH at 50 °C. Single particles of this CoNiFeCu after their placement on nanoelectrodes combined with identical location transmission electron microscopy before and after applying cyclic voltammetry are investigated. The improved catalytic performance is due to surface carbon corrosion and Cu leaching. The proposed catalyst design strategy combined with the unique single-nanoparticle technique contributes to the development and characterization of high-performance catalysts for electrochemical energy conversion. ; This research was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) within the collaborative research center/transregio 247 "Heterogeneous Oxidation Catalysis in the Liquid Phase" TRR 247 [388390466] as well as under Germanys Excellence Strategy—EXC 2033-390677874—RESOLV. The project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant Agreement CasCat [833408]). J.Z. acknowledges the Chinese Scholarship Council for a Ph.D. fellowship. This work was supported by the "Center for Solvation Science ZEMOS" funded by the German Federal Ministry of Education and ...

16 figures, 6 tables.-- Supplementary material available. ; Ceria-iron oxide mesoporous materials with Fe:Ce molar ratio of 5:5 and 9:1 were synthesized by hydrothermal method using CTAB as a template and subsequently modified with NiO (molar ratio Ni:Fe = 1:2) by incipient wetness impregnation technique. In order to increase the electro-capacitive properties and reduce the intrinsic impedance of the metal oxides, the samples were consecutively modified by reduction in hydrogen to obtain highly dispersed Ni–Fe alloys into ceria matrix. By exploiting the high permeability of carbon inside ferrous alloys, the metal phase has been further modified into ferrous carbides and metal alloys encapsulated within carbon nanofibers. For this purpose, a reaction, already widely studied for the production of hydrogen, was used, that is the decomposition of methanol vapors. In fact, this decomposition, in addition to producing syn-gas and methane, changes the catalysts in use through a chemical vapor deposition-carbon coating process. This fact, has been used by us to demonstrate how the newly obtained metal-carbon nanocomposites can be used for electro-catalytic purposes. The modified phases of the two molar ratios of the Fe–Ni–Ce catalysts were tested in the Oxygen Evolution Reaction (OER) in an alkaline environment (1 M KOH), showing a satisfactory and progressive increase in activity and a surprising decrease in the overpotential at 10 mA/cm2 of current density. The morphological, textural and physicochemical properties of the samples were characterized in details by XRD, N2-physisorption, TG-TPO, TEM, EDX, FTIR, XPS, Raman and Moessbauer spectroscopies. ; This research was funded by the BIKE project, which received funding from the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement no. 813748. ; Peer reviewed

11 figures, 2 tables.-- Supplementary information available. ; Electrochemical water splitting is an environmentally benign technology employed for H2 production; however, it is critically hampered by the sluggish kinetics of the oxygen evolution reaction (OER) at the positive electrode. In this work, nitrogen-doped carbon-coated CoFe electrocatalysts were synthesized via a three-step route comprising (1) hydrothermal reaction, (2) in-situ polymerization of dopamine and (3) carbonization. The effect of carbonized polydopamine on the overall physicochemical properties and electrochemical activity of CoFe catalysts was systematically studied. By controlling and optimizing the ratio of CoFe2O4 and dopamine contents, a transformation of the CoFe2O4 structure to CoFe alloy was observed. It was found that CoFe/NC30% (prepared with 30% dopamine) exhibits an excellent catalytic activity towards OER. A small overpotential of 340 mV was required to generate a current density of 10 mA cm-2 in a 1.0 M KOH electrolyte. More importantly, the CoFe/NC30% catalyst reflected exceptional durability for at least 24 h. This research sheds light on the development of affordable, highly efficient, and durable electrocatalysts for OER. ; Financial support from the European Union's Horizon 2020 Research and Innovation programme under the Marie Skłodowska-Curie Actions-Innovative Training Networks (MSCA-ITN) Grant Agreement 813748 are gratefully acknowledged. The authors wish to acknowledge the grants PID2020-115848RB-C21 and PID2020-115848RB-C22 funded by MCIN/AEI/10.13039/501100011033. ; Peer reviewed