Developing nonprecious oxygen evolution electrocatalysts that can work well at large current densities is of primary importance in a viable water-splitting technology. Herein, a facile ultrafast (5 s) synthetic approach is reported that produces a novel, efficient, non-noble metal oxygen-evolution nano-electrocatalyst that is composed of amorphous Ni-Fe bimetallic hydroxide film-coated, nickel foam (NF)-supported, Ni S nanosheet arrays. The composite nanomaterial (denoted as Ni-Fe-OH@Ni S /NF) shows highly efficient electrocatalytic activity toward oxygen evolution reaction (OER) at large current densities, even in the order of 1000 mA cm . Ni-Fe-OH@Ni S /NF also gives an excellent catalytic stability toward OER both in 1 m KOH solution and in 30 wt% KOH solution. Further experimental results indicate that the effective integration of high catalytic reactivity, high structural stability, and high electronic conductivity into a single material system makes Ni-Fe-OH@Ni S /NF a remarkable catalytic ability for OER at large current densities.

The overall water splitting into hydrogen and oxygen is one of the most promising ways to store intermittent solar and wind energy in the form of chemical fuels. However, this process is quite thermodynamically uphill, and thus needs to be mediated simultaneously by efficient hydrogen evolving and oxygen evolving catalysts to get any feasible output from it. Herein, we report the synthesis of such a catalyst comprising ultrasmall Ni x Co 3-x S 4 -decorated Ni 3 S 2 nanosheet arrays supported on nickel foam (NF) via a partial cation exchange reaction between NF-supported Ni 3 S 2 nanosheet arrays and cobalt(II) ions. We show that the as-prepared material, denoted as Ni x Co 3-x S 4 /Ni 3 S 2 /NF, can serve as a selfstanding, noble metal-free, highly active and stable, bifunctional electrocatalyst for the two half reactions involved in the overall water splitting: the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Furthermore, we demonstrate that a high-performance electrolyzer for the overall water splitting reaction can be assembled by using Ni x Co 3-x S 4 /Ni 3 S 2 /NF as the electrocatalyst at both the cathode and the anode sides of the electrolyzer. This electrolyzer delivers water-splitting current densities of 10 and 100 mA/cm 2 at applied potentials of 1.53 and 1.80 V, respectively, with remarkable stability for >200 h in both cases. The electrolyzer's performance is much better than the performances of electrolyzers assembled from many types of other bifunctional electrocatalysts as catalyst couple. Moreover, the overall performance of the electrolyzer is comparable with the performances of electrolyzers containing two different, benchmark, monofunctional HER and OER electrocatalyst couple (i.e., Pt/C-IrO 2 ). Keywords： Water splitting • Nickel sulfide • Cobalt sulfide • Electrocatalysis • Composite materialDe-jun Wang received his Ph. D. from Jilin University in 1989. He then worked as a Postdoctoral researcher at Kyoto University for 1 year since 1989-1990. In 1992, he joined Jilin University as a staff. He is currently a Professor in the College of Chemistry, Jilin University. His research interests include surface photovoltage technology, photoelectric sensors, photoelectrochemical water splitting and solar cells.

Understanding of catalytic trends is an important prerequisite for providing rational guidance toward the prediction of advanced catalysts as well as the development of original materials design principles. A combined theoretical and experimental study that reveals the periodic trends in electrocatalytic activity for the hydrogen evolution reaction (HER) from Group IV B to Group VIII metal diborides is reported here. Theoretical results demonstrate a general linear relationship between the catalytic activity and d‐band center of metal diboride, meaning that the latter can serve as a descriptor of activity. And theoretical results also predict ruthenium diboride as the most competitive, nonplatinum candidate among metal diborides for HER because this material has a suitable d‐band center and a high density of efficient active sites. Furthermore, the experimental results validate the theoretical activity trends and identify ruthenium diboride as an efficient, pH‐universal electrocatalyst with Pt‐like activity for HER under both acidic and alkaline media.

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In low-dimensional systems with strong electronic correlations, the application of an ultrashort laser pulse often yields novel phases that are otherwise inaccessible. The central challenge in understanding such phenomena is to determine how dimensionality and many-body correlations together govern the pathway of a non-adiabatic transition. To this end, we examine a layered compound, 1T-TiSe2, whose three-dimensional charge-density-wave (3D CDW) state also features exciton condensation due to strong electron-hole interactions. We find that photoexcitation suppresses the equilibrium 3D CDW while creating a nonequilibrium 2D CDW. Remarkably, the dimension reduction does not occur unless bound electron-hole pairs are broken. This relation suggests that excitonic correlations maintain the out-of-plane CDW coherence, settling a long-standing debate over their role in the CDW transition. Our findings demonstrate how optical manipulation of electronic interaction enables one to control the dimensionality of a broken-symmetry order, paving the way for realizing other emergent states in strongly correlated systems.