Preparation Of Cobalt-based Phosphorous Nanomaterial And Their Electrochemical Hydrogen Evolution

The demand for clean energy?such as solar,wind and hydro?as an alternative to fossil fuels is growing due to natural fossil fuels and current global environmental crises,which has been widely recognized as the only one that ensures world economic and social sustainable development Feasible approach.Therefore,It is especially important to develop efficient,environmentally friendly energy conversion and storage technologies.Hydrogen production is an attractive solution for sustainable energy storage.Hydrogen has proven its energy as an ideal energy carrier for a sustainable energy economy because of its high energy density and environmental friendliness.The transition metal?iron,cobalt,nickel,etc.?materials have good electrocatalytic properties.For example,transition metal phosphides,sulfides,selenides and other applications are well used in electrochemical hydrogen evolution.In this paper,cobalt phosphide hollow nanosphere materials,cobalt-nickel phosphide nickel hollow nanosheet composites and basic cobalt carbonate nanoplates were prepared and their morphology,composition and structure were analyzed.Finally,their hydrogen evolution performance in electrolysis was studied.The main conclusions are as follows:?1?The development of low-cost and high-efficiency electrocatalysts for the hydrogen evolution reaction?HER?by morphology and structure modulations have attracted increasing interest.Herein,when directly used as a cathode for electrochemical hydrogen evolution,CoP-60 hierarchical structure electrode exhibited high performance with overpotential???of 147 m V to achieve the current densities?j?of 10 mA cm^-2,small Tafel slope of 56 m V dec^-1,and good stability under acidi-conditions,which were synthesized by a tow-step solvothermal method and One-step calcination.Control of the morphology by adjusting different volumes of deionized and ethanol showed different hydrogen evolution reactions.Additionally,this electrode provides a way to synthesize transition metal phosphides?TMPs?for catalysis.?2?A series of Ni _XCo_1-XG?0?x?1?were prepared by using the solid Ni _XCo_1-XG nanospheres as the precursor template,the Ni-Co glycerate(Ni _XCo_1-XG)nanospheres composed of ultrathin nanosheets were fabricated in water mixed solution via a hydrothermal reaction.Ni_XCo_1-XG nanospheres with varied Ni:Co atom ratios were synthesized by simply varying the original molar ratios of Ni:Co in the precursors to synthesize various products.After phosphating the precursors with NaH₂PO₂ in N₂atmosphere,the hierarchical Ni_XCo_1-XP nanospheres were obtained.The best performance was found with the catalyst Ni_0.33Co_0.67P.Owing to the unique ultrathin subunits,the as-prepared Ni_XCo_1-XP nanospheres exhibit high performance with overpotential of 146mV to achieve the current densities of 10 mA cm^-2,small Tafel slope of 61 mV dec^-1,and good stability under acidi-conditions.This work may provide an effective strategy to fabricate delicate hierarchical nanostructure HER electrocatalysts.?3?The most common strategy to synthesize transition metal phosphides?TMPs?was phosphidation treatment of the precursor with NaH₂PO₂ in nitrogen atmosphere.In a sense,this phosphating process greatly affected the surface state and chemical composition of TMPs,which were crucial to catalytic activity for hydrogen evolution reaction?HER?.In this study,it was demonstrated that the pristine product synthesized via such low-temperature phosphorization of cobalt hydroxide carbonate?Co₂?OH?₂CO₃?microsheets?MSs?precursor was composed of Co_xP and amorphous cobalt phosphate?a-CoPi?.However,a-CoPi component in obtained TMPs was often neglected due to the limitation of XRD in detecting amorphous phase.Actually,a-CoPi and CoxP were conformally decorated on MSs.The a-CoPi component covered numerous active sites,leading to degradation of HER performance.Through a simple acid treatment,a-CoPi components could be effectively removed,which brought about 3.5-fold enhancement of HER activity.This study not only revealed that the conventional low-temperature phosphating route might introduce abundant amorphous phosphate in obtained product,but also afforded an effective strategy for improving the HER activity,which might provide guidance for the synthesis of highly efficient HER catalysts.