| The demand for sustainable energy is increasing sharply with the growth of the world population.As a green sustainable energy,hydrogen energy is considered as the most promising green clean energy.Electrochemical catalyzing water splitting has been viewed as one feasible and easily-implemented method to produce hydrogen energy.Electrocatalysis of water splitting consists of two half-reactions,i.e.hydrogen evolution reaction（HER）in cathode and oxygen evolution reaction（OER）in anode.Precious metals（Pt）and metal oxides（e.g.,IrO2 and RuO2）are considered to be the state-of-the-art electrocatalysts for HER and OER,respectively.However,the practical application of these precious metal based electrocatalysts has been greatly restricted by their high cost and scarcity.Therefore,it is highly desirable to develop bifunctional electrocatalysts for both HER and OER.The key principle for the design of efficient and durable water splitting eletrocatalyst lies in a large number of active sites,excellent conductivity and stable catalytic activity structure.Based on the above several design principles,the main contents of this paper are as follows:（1）We report a reliable and facile anion-exchange reaction strategy for conversion of one-dimensional（1D）Co3O4 nanowires（NWs）into CoP porous nanowires（PNWs）.Notably,such evolution process provides the as-formed CoP PNWs with significantly improved defect sites and thus endows the CoP PNWs with a high electrochemical activity surface area.Accordingly,the CoP PNWs exhibit outstanding catalytic activity toward HER and OER when serving as bifunctional electrocatalysts,achieving a current density of 10 mA cm-2 with low overpotentials of 147 and 326 mV for HER and OER,respectively.We demonstrate the water splitting electrolyzer with such CoP PNWs electrocatalyst as cathode and anode can be driven by a double A battery（1.5 V）.The advantages,including facile and low-cost synthetic process,high activity for HER and OER,endow the as-developed CoP PNWs to be one of the most promising candidates for full water splitting system.（2）We herein report a Ru-RuO2/CNTs nanohybrid that shows ultrahigh activity toward hydrogen/oxygen evolution reaction in pH-universal electrolyte.Systematic characterizations and theoretical calculation verify that Ru likely synergistically works with RuO2 and CNTs to contribute such desirable electrocatalytic activity.The Janus catalytic properties,in conjunction with its pH-universal compatibility,inspire us to set up an asymmetric-electrolyte electrolyzer that can harvest the electrochemical neutralization energy,which can deliver a current density of 10 mA cm-2 at an applied voltage of 0.73 V,even much lower than the theoretical thermodynamic voltage（1.23V）required in a conventional water electrolysis system,signifying reduction of energy consumed in half provided the inevitable overpotential in a conventional water electrolyzer. |
