In Situ Synthesis Of Cu-based Nanoarray Electrode And Its Electrocatalytic Water Splitting Performance

Producing hydrogen with high purity by electrolysis of water is one of the most effective ways to obtain clean and renewable energy.Platinum group materials such as IrO₂,RuO₂ and Pt are the state-of-the-art catalysts for electrochemical water splitting,but the high prices and scarcity hinders their large-scale industrial applications greatly.Consequently,transition metal materials,due to their rich redox property and abundant electron orbitals,has became a hotspot in electrocatalysis.Their oxides（hydroxides）,sulfides,phosphides and alloys in nanoscale show outstanding activity toward oxygen evolution reaction（OER）,hydrogen evolution reaction（HER）and full water splitting.In this work,a series of Cu-based nanoarray materials were designed,synthesized and applied in water splitting using the copper foam or copper foil as both the substrate and Cu source directly,these catalysts were optimized through surface modification,morphological adjustment and interface regulation to improve the electrocatalytic performance.Meanwhile,these works provided new ideas for the application of copper based nano-catalysts in other catalytic fields.The details of this work are summarized as follows:Chapter 1:A mini review about the electrochemical water splitting,including the evaluation parameters of water splitting,the mechanism of HER and OER half reactions,and application of Cu-based materials toward electrocatalytic water splitting.Chapter 2:A layer of NiFe-LDH film was deposited on the surface of CuO nanorods by a chronopotentiometry deposition method.The molar ratios of Ni and Fe salts and the deposition time were changed to study the influence on the deposition of NiFe-LDH on CuO NRs.The current density of NiFe-LDH/CuO NRs can reach 50 mA cm^-22 in 1 M KOH for OER at a overpotential of 290 mV,the Tafel slope value of 60 mV dec^-11 was obtained.The NiFe-LDH/CuO NRs was able to continuous electrolysis for at least 35 h,outperforming the activities of its NiFe-LDH and CuO counterpart.Chapter 3:The cyclic voltammetry scanning（CV）method was used to grow a layer of CoP on the CuO surface to obtain the CuO-FR@CoP with three-dimensional hierarchical morphology which is composed of interlaced CuO-FR@CoP micro-flowers and nanorods.The scan cycle and the molar ratios of Co and P precursors were changed to optimize the preparation condition and the electrocatalytic performance of CuO-FR@CoP.CuO-FR@CoP requires an overpotential of 290mV to deliver a current density of 50 mV cm² toward water oxidation in alkaline media,and maintained the catalytic activity for at least 30 h with a Faraday efficiency of 98%.The catalytic efficiency of CuO-FR@CoP is much higher than that of CuO without modification.Chapter 4:The CuO_x@Co₃O₄ NRs core-shell structure was obtained by a hydrothermal and an annealing process.The electrode exhibits excellent OER and HER catalytic activity in 1 M KOH,which resulted in a small overpotential of 240 mV for the OER and 242 mV for the HER at a current density of 50 mA cm^-2,along with low Tafel slopes of 46 and 61 mV dec^-1,respectively.CuO_x@Co₃O₄ NRs/CF also could continuously produce O₂ or H₂ for at least 24 h with negligible decline in catalytic activity.The outstanding activity can be attributed to its unique three-dimensional morphology with large surface area and abundant catalytic active site,and the strong synergistic effect between CuO_x core and Co₃O₄ shell.Chapter 5:Cu（OH）₂ NRs@Co₂CO₃（OH）₂ precursor was sulfurized to Cu₂S NRs@CoS core-shell structure in room temperature,the surface of Cu₂S core was covered by a layer of CoS nanosheets arrays.When employed as bifunctional catalyst,Cu₂S NRs@CoS was able to reach the current density of 50 mA cm^-22 at the overpotential of 275 mV in 1 M KOH with the Tafel slope of54 mV dec^-11 toward OER.As for HER,Cu₂S NRs@CoS need 235 mV to reach the same current density,rivalling the performance of Cu₂S and CoS counterparts.The excellent catalytic activity of Cu₂S NRs@CoS can be attributed to the in-situ synthetic method,the synergistic effects in Cu₂S/CoS interface and the smart hierarchical morphology.Chapter 6:A conclusion and prospect of this work.