Preparing efficient and robust water oxidation catalyst (WOC) with inexpensive materials remains a crucial challenge in artificial photosynthesis and for renewable energy. Existing heterogeneous WOCs are mostly metal oxides/hydroxides immobilized on solid supports. Herein we report a newly synthesized and structurally characterized metal-organic hybrid compound [{Co3 (μ3 -OH)(BTB)2(dpe)2} {Co(H2O)4(DMF)2}0.5]n ⋅n H2O(Co-WOC-1) as an effective and stable water-oxidation electrocatalyst in an alkaline medium. In the crystal structure of Co-WOC-1, a mononuclear Co(II) complex {Co(H2O)4(DMF)2}(2+) is encapsulated in the void space of a 3D framework structure and this translationally rigid complex cation is responsible for a remarkable electrocatalytic WO activity, with a catalytic turnover frequency (TOF) of 0.05 s(-1) at an overpotential of 390 mV (vs. NHE) in 0.1 m KOH along with prolonged stability. This host-guest system can be described as a "ship-in-a-bottle", and is a new class of heterogeneous WOC.

Massive strandings of the pelagic brown algae Sargassum have occurred in the Caribbean, and to a lesser extent, in western Africa, almost every year since 2011. These events have major environmental, health, and economic impacts in the affected countries. Once on the shore, Sargassum is mechanically harvested and disposed of in landfills. Existing commercial applications of other brown algae indicate that the pelagic Sargassum could constitute a valuable feedstock for potential valorisation. However, limited data on the composition of this Sargassum biomass was available to inform on possible application through pyrolysis or enzymatic fractionation of this feedstock. To fill this gap, we conducted a detailed comparative biochemical and elemental analysis of three pelagic Sargassum morphotypes identified so far as forming Atlantic blooms: Sargassum natans I (SnI), S. fluitans III (Sf), and S. natans VIII (SnVIII). Our results showed that SnVIII accumulated a lower quantity of metals and metalloids compared to SnI and Sf, but it contained higher amounts of phenolics and non-cellulosic polysaccharides. SnVIII also had more of the carbon storage compound mannitol. No differences in the content and composition of the cell wall polysaccharide alginate were identified among the three morphotypes. In addition, enzymatic saccharification of SnI produced more sugars compared to SnVIII and Sf. Due to high content of arsenic, the use of pelagic Sargassum is not recommended for nutritional purposes. In addition, low yields of alginate extracted from this biomass, compared with brown algae used for industrial production, limit its use as viable source of commercial alginates. Further work is needed to establish routes for future valorisation of pelagic Sargassum biomass.

A cobalt complex bearing a redox-active monoanionic amidate ligand is shown to act as an efficient molecular electrocatalyst for water oxidation at a moderate overpotential (∼500 mV) in mildly alkaline medium.

The design and synthesis of an efficient and robust water-oxidation catalyst with inexpensive materials remains an important challenge in the context of artificial photosynthesis. Herein, as imple but unique technique is reported to in situ generate at hin-film of a-Co(OH) 2 on the surface of zeolite-Y [hereafter referred to as Y-a-Co(OH) 2 ] that acts as an efficient and stable catalyst for electrochemical water oxidation in alkaline medium. Catalyst Y-a-Co(OH) 2 is so stable that it retains its catalytic activity even after 2000 cyclic voltammetric cycles of water oxidation. Expectedly,t he chemical compositiono fa-Co(OH) 2 on the surface of zeolite-Y remainss ame as that of parentY -a-Co(OH) 2 after 2000 electrocatalytic cycles. AT afel slope as low as 59 mV decade À1 in 0.1 m KOH (pH 13) suggestsf aster oxygen evolution kinetics (overpotential = 329 mV;t urnover frequency = 0.35 mol O 2 (mol Co)À1 s À1 at 1mAcm À2 )t han the existing aCo(OH) 2 -based electrocatalysts operating in alkaline medium.

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