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The electrochemical two-electron oxygen reduction reaction (2e− ORR) for the production of hydrogen peroxide (H2O2) enables a promising electro-Fenton process for on-site and on-demand environmental remediation. However, there is still a lack of low-cost electrocatalysts for efficient H2O2 electrosynthesis, particularly in acidic media. Herein, we designed and synthesized cobalt species incorporated in oxygen-rich mesoporous carbon nanosheets (MesoC-Co), resulting in electrochemical H2O2 production with a selectivity above 80% over a wide potential range in 0.10 M HClO4. In our reported electrocatalysts, atomic Co sites contribute to the high ORR activity of carbon-based materials in an acidic medium, and the oxygen-containing functional groups and mesoporous structure endow the catalysts with high H2O2 selectivity. The ORR current density over MesoC-Co with uniform mesopores and well-defined Co species reaches −1 mA cm−2 at 0.4 V versus reversible hydrogen electrode with very good durability. In addition, the cumulative concentration of H2O2 is 7.2 mmol L−1 within 24 h, allowing for the effective electro-Fenton degradation of organic pollutants. Our results might shed light on the design of catalytic systems for sustainable electro-Fenton processes. [ABSTRACT FROM AUTHOR]

The development of highly efficient oxygen evolution reaction (OER) electrocatalysts is critical because the sluggish reaction kinetics of this reaction usually hinders the efficiency of water electrolysis for the generation of H2. Herein, we report that ultrathin cobalt-based coordination polymers (Co-CPs) plates are exceptional electrocatalysts for the OER as they show one of the most lowest Tafel slopes among the cobalt-based OER catalysts reported to date. It has been found that the Co-CPs can be transformed into Co(OH)2 hexagonal nanoplates and then further oxidized into CoOOH, which acts as a catalytic active site for the oxidation of water. Interestingly, when Ca2+, an inactive ion, was introduced into the precursors, thinner CoOOH nanosheets with more exposed active sites were formed, which displayed significantly higher OER activity than the Co-CPs. Furthermore, the content of Ca2+ in the Co-based coordination polymers (CoxCay-CPs) and the corresponding OER activity of these CPs were systematically investigated, and Co0.89Ca0.11-CPs exhibited highest OER activity. This study provides a fundamental understanding of the catalytic mechanism of cobalt-based coordination polymer electrocatalysts and the effect of inactive species, such as Ca2+, on the OER in an alkaline electrolyte, which may promote the design of highly active electrocatalysts. [ABSTRACT FROM AUTHOR]

Herein, we report the promotion effect of ZnO in water oxidation catalyzed by Co. Zinc–cobalt oxides―ZnCoxOy were prepared via the calcination of Zn–Cox-coordination polymers. The results of XRD, Co K-edge XANES and EXAFS show that the Co/Zn ratio greatly affected the oxidation state of Co and local structure of the ZnCoxOy oxides. With a Co/Zn ratio higher than 3.0, Zn(ii) prefers to substitute in the lattice of Co3O4. The integrated ZnO and Co3O4 composites were formed at a Co/Zn ratio less than 2.0. The HR-TEM images show that ZnO and Co3O4 compactly contact to form the interfaces in the composites. In both the chemical water oxidation and the visible-light-driven photocatalytic water oxidation ([Ru(bpy)3]2+–persulfate system), Zn substituted in the spinel structured Co3O4 oxide cannot significantly improve the water oxidation activity and only the integrated ZnO and Co3O4 composites afford much higher TOFs than Co3O4. This suggests the existence of the cooperation effect between ZnO (water adsorption site) and Co3O4 (water oxidation site). Our results provide a facile approach to design composite catalysts for the water oxidation reaction. [ABSTRACT FROM AUTHOR]

Co3O4 with high capacities and energy density has potential applications to be electrode materials for lithium ion batteries, one of the most important power sources. For improving the cycling stability, the Co3O4 nanostructures are required. Herein, we report successful construction of Co3O4 hexagonal nanorings and nanoplates/nanoparticles via treating Co-based metal organic frameworks (MOFs) with organic amine. The studies show that the release rate of Co(II) to the reaction system and the spatial hindrance of the organic linkers of MOFs determine the final morphology of Co3O4. As an anode for lithium ion batteries, Co3O4 hexagonal nanorings with 1370 mA h g-1 specific capacity after 30 cycles displayed higher reversible capacity and better stability than commercial Co3O4 particles with only 117 mA h g-1 specific capacity after 30 cycles. The improved performance of Co3O4 hexagonal nanorings could be attributed to the shortened transfer path for Li+ afforded by the special morphology. It is expected that plentiful metal oxide nanostructures could be constructed from MOFs due to the available versatile categories of MOFs. [ABSTRACT FROM AUTHOR]

The development of non-precious metal catalysts for oxygen reduction reactions (ORRs) is of extreme importance for the construction of efficient H2/O2 polymer electrolyte membrane fuel cells (PEMFCs), one of the most promising clean energy technologies. Herein, we report the fabrication of core-shell structured CNTs@Fe-N-C composites with a Fe-N-C shell closely wrapped around a core of CNTs (carbon nanotubes) as efficient catalysts for ORR. CNTs@Fe-N-C composites afford comparable activity to commercial Pt/C catalysts with a loading of 20 μg Pt cirT2 towards ORR in alkaline media. The results of XRD, TEM, XPS and 57Fe Mössbauer characterizations suggest that the high ORR activity of CNTs@Fe- N-C composites are mainly attributed to the combined advantages of the unique core-shell nanostructure allowing close contact between Fe-N-C and CNTs, uniformly distributed FeN4/C species, and the presence of pyridine and graphitic nitrogen. [ABSTRACT FROM AUTHOR]

The electrochemical reduction of carbon dioxide (CO 2 ) has attracted considerable attention as a means of maintaining the carbon cycle. This process still suffers from poor performance, including low faradaic efficiencies and high overpotential. Herein, we attempted to use coordination number as a control parameter to improve the electrocatalytic performance of metal species that have previously been thought to have no CO 2 reduction activity. Covalent triazine frameworks (CTF) modified with coordinatively-unsaturated 3d metal atoms (Co, Ni or Cu) were developed for efficient electroreduction of CO 2 . Co-CTF and Ni-CTF materials effectively reduced CO 2 to CO from -0.5 V versus RHE. The faradaic efficiency of the Ni-CTF during CO formation reached 90% at -0.8 V versus RHE. The performance of Ni-CTF is much higher than that of the corresponding metal-porphyrin (using tetraphenylporphyrin; TPP). First principles calculations demonstrated that the intermediate species (adsorbed COOH) was stabilized on the metal atoms in the CTF due to the low-coordination structure of this support. Thus, the free energy barriers for the formation of adsorbed COOH on the metal atoms in the CTF supports were lower than those on the TPP supports.

Mesoporous graphitic carbon nanodisks with hierarchical porous structure, facilely fabricated by catalytic carbonization of iron-based coordination polymer nanodisks, exhibit high capacitance even at high scan rates as electrode materials for electrochemical double layer capacitors.