The present report uncovers the borderline between homogeneous and heterogeneous water oxidation catalysis using a family of Ni complexes containing oxamidate anionic type of ligands. In particular, the Ni complex [(L 1)Ni II ] 2-(1 2-; L 1 = o-phenylenebis(oxamidate)) and its modified analogues [(L 2)Ni II ] 2-(2 2-;L 2 = 4,5-dimethyl-1,2-phenylenebis(oxamidate)) and [(L 3)Ni II ] 2-(3 2-;L 2 = 4methoxy-1,2-phenylenebis(oxamidate)) have been prepared and evaluated as molecular water oxidation catalysts at basic pH. Their redox features have been analyzed by mean of electrochemical measurements revealing a crucial involvement of the ligand in the electron transfer processes. Moreover, the stability of those complexes has been assessed both in solution and immobilized on graphene-based electrodes at different potentials and pHs. The degradation of the molecular species generates a NiOx layer, whose stability and activity as water oxidation catalyst has also been stablished. Electrochemical methods, together with surface characterization techniques, have shown the complex mechanistic scenario in water oxidation catalyzed by this family of Ni complexes, which consists of the coexistence of two catalytic mechanism: a homogeneous pathway driven by the molecular complex and a heterogeneous pathway based on NiOx. The electronic perturbations exerted through the ligand framework has manifested a strong influence over the stability of the molecular species under turnover conditions. Finally, 1 2has been used as a molecular precursor for the formation of NiFeOx anodes that behave as extremely powerful water oxidation anodes.

Figure 8. Intermolecular vs. intramolecularH ÀHb ondformation. Transition states (TS) relevant to the hydrogen evolution reaction by catalysts 1-3.T he kinetic barriers (DG°)are indicated for each catalyst in kcal mol À1 and representative drawings of each TS is given for 1. DG°= G(TS)ÀG(Co II ÀH), see moredetails in the SupportingI nformation.Scheme1.Catalytic pathways towards hydrogen evolution by catalysts 1-3.RDS:rate determining step of the process.

We study the optimization of the catalytic properties of entirely magnetic CoPt compact and mesoporous nanowires of different diameters (25 -200 nm) by using magnetic actuation. The nanowires are a single-entity, robust, magnetic-catalyst with a huge catalytically-active surface area.We show that apart from conventional parameters, like the size and morphology of the nanowires, other 2 factors can be optimized to enhance their catalytic activity. In particular, given the magnetic character of the nanowires, rotating magnetic fields are a very powerful approach to boost the performance of the catalyst. In particular, the magnetic field induces them to act as nano-stirrers, improving the local flow of material towards the active sites of the catalyst. We demonstrate the versatility of the procedure by optimizing (i) the degradation of different types of pollutants (4-nitrophenol and methylene blue) and (ii) hydrogen production. For example, by using as little as 0.1 mg mL -1 of 25 nm wide CoPt mesoporous nanowires (with 3 nm pore size) as catalysts, kinetic normalized constants knor as high as 20667 and 21750 s -1 g -1 for 4-nitrophenol and methylene blue reduction, respectively, are obtained. In addition, activity values for hydrogen production from borohydride are as high as 25.0 L H2 g -1 min -1 , even at room temperature. These values outperform any current state-of-the-art proposed catalysis strategies for water remediation reactions by at least 10-times and are superior to most advanced approaches to generate hydrogen from borohydride. The recyclability of the nanowires together with the simplicity of the synthetic method makes this approach (using not only CoPt, but also other mesoporous magnetic catalysts) very appealing for very diverse types of catalytic applications. Graphical AbstractHighlights  Magnetic actuation of purely magnetic mesoporous nanowires (NWs) is revealed as a novel and efficient catalysis procedure in reactions of heterogeneous catalysis in environmental and energy fields. Mesoporous CoPt NWs are simultaneously effective catalysts itself and the stirring device, using magnetic fields, to catalyse reactions in solution. The procedure allows ultra-fast degradation of different types of pollutants. 3 The NWs show very high effectivity for hydrogen generation (25.0 L H2 g -1 min -1 ) by catalysing the hydrolysis of sodium borohydride using magnetic actuation.

A hybrid photoanode, made of a multilayered heterostructured WO3/BiVO4 semiconductor, a carbon nanotube fibre and a rugged and highly active molecular water oxidation catalyst is described.