The development of cost-effective oxygen evolution catalysts is of capital importance for the deployment of large scale energy storage systems based on metal-air batteries and reversible fuel cells. In this direction, a wide range of materials have been explored, especially in more favorable alkaline conditions, and several metal chalcogenides have particularly demonstrated excellent performances. However, chalcogenides are thermodynamically less stable than the corresponding oxides and hydroxides under oxidizing potentials in alkaline media. While this instability in some cases has prevented the application of chalcogenides as oxygen evolution catalysts, and it has been disregarded in some other, we propose to use it in our favor to produce high performance oxygen evolution catalysts. We characterize here the in situ chemical, structural and morphological transformation during the oxygen evolution reaction (OER) in alkaline media of Cu2S into CuO nanowires (NWs), mediating the intermediate formation of Cu(OH)2. We also test their OER activity and stability under OER operation in alkaline media, and compare them with the OER performance of Cu(OH)2 and CuO nanostructures directly grown on the surface of a copper mesh. We demonstrate here that CuO produced during OER from Cu 2 S displays an extraordinary electrocatalytic performance toward OER, well above that of CuO and Cu(OH)2 synthesized mediating no OER in situ transformation.3

The inhibition of this polysulfide shuttle effect and the promotion of the redox reaction kinetics remains as the key material challenges of lithium-sulfur batteries (LSBs) to be urgently solved.Here we report a new architecture for the cathode material based on nanoreactor of ZnSe/Ndoped hollow carbon (ZnSe/NHC). This material combination and the hollow geometry provide three key benefits to the LSBs cathode: i) The combination of lithiophilic sites of NHC and sulfiphilic sites of ZnSe effectively trap LiPS as demonstrated by experimental results and density functional theory (DFT) calculations; ii) In part related to this promoted adsorption, the ZnSe/NHC material combination is able to facilitate the Li + diffusion, thus promoting the redox reaction kinetics; iii) The hollow nanoreactor design traps LiPS and accommodates volumetric expansion preventing the cathode material decomposition. As a result, LSBs cathodes based on this hybrid material, S@ZnSe/NHC, are characterized by high initial capacities, 1475 mAh g −1 at 0.1 C and 542 mAh g −1 at 3 C, and excellent rate capability. Besides, these cathodes deliver stable operation with only 0.022% capacity decay per cycle after 800 cycles at 3 C. Even at high sulfur loading of 3.2 mg cm −2 , a reversible capacity of 540.5 mAh g −1 is delivered after 600 cycles at 1 C. Overall, this work not only further demonstrates the large potential of transitionmetal selenides as cathode materials in LSBs, but also demonstrates the nanoreactor design to be a highly suitable architecture to enhance cycle stability.

Graphical abstract Scheme 1. NiSn nanoparticles towards methanol oxidation reactions Highlights A new colloidal synthesis route for 3-5 nm NiSn bimetallic nanoparticles with tuned Ni/Sn ratio was developed. The first study of the performance of NiSn as electrocatalysis of methanol oxidation reaction (MOR) is presented. NiSn electrodes showed excellent performance towards MOR, with the most Ni-rich alloy exhibiting mass current densities of 820 mA mg -1 at 0.70 V vs. Hg/HgO, comparable to state of the art Ni electrocatalysts. Stability of NiSn electrodes was clearly superior to that of Ni-based electrodes. NiNi 2+ CH 3 OH Ni 3+Products e e e e e e e e e e e e e e e e e e e e e e e e e e AbstractNickel is an excellent alternative catalyst to high cost Pt and Pt-group metals as anode material in direct methanol fuel cells. However, nickel presents a relatively low stability under operation conditions, even in alkaline media. In this work, a synthetic route to produce bimetallic NiSn nanoparticles (NPs) with tuned composition is presented. Through co-reduction of the two metals in the presence of appropriate surfactants, 3-5 nm NiSn NPs with tuned Ni/Sn ratios were produced. Such NPs were subsequently supported on carbon black and tested for methanol electro-oxidation in alkaline media. Among the different stoichiometries tested, the most Ni-rich alloy exhibited the highest electrocatalytic activity, with mass current density of 820 mA mg -1 at 0.70 V (vs. Hg/HgO). While this activity was comparable to that of pure nickel NPs, NiSn alloys showed highly improved stabilities over periods of 10000 s at 0.70 V. We hypothesize this experimental fact to be associated to the collaborative oxidation of the byproducts of methanol which poison the Ni surface or to the prevention of the tight adsorption of these species on the Ni surface by modifying its surface chemistry or electronic density of states.