| With the rapid development of human society,energy shortage and water pollution have become two serious problems for human society.Therefore,there is an urgent need to solve the problems by the development of clean new energy sources and effective treatment method of pollutants in water.Hydrogen is regarded as an ideal alternative to high-polluting fossil fuels.Electrocatalytic water splitting to produce hydrogen is one of the promising methods for hydrogen generation.However,there are two key problems to be solved urgently in hydrogen production by electrolysis of water.First of all,both the hydrogen evolution reaction?HER?on cathode and the oxygen evolution reaction?OER?on anode need high overpotential,so the energy consumption of electrolytic water splitting is high.Moreover,OER on anode is not only the limiting step for overall water splitting,but also the added value of oxygen production by OER is low.In order to solve the two problems mentioned above,there are two effective ways.On the one hand,electrocatalysts with high catalytic activity are designed and synthesized to reduce the overpotential for cathodic HER and anode OER.On the other hand,a composite electrolytic cell is constructed by employing thermodynamically more favorable and higher economic valuable to replace sluggish OER with cathodic HER to reduce the whole required voltage.Therefore,this work mainly aims at reducing the voltage of electrolysis of water and energy consumption.From the two aspects mentioned above,the optimization of the water splitting composite system and the catalytic activity of the electrode were studied.On the one hand,the ruthenium ions in water was adsorbed and recycled by saccharomycete,which was dealed by two ways to obtain the different electrocatalysts for cathode hydrogen production and the anode oxygen production,respectively.Hydrogen production by overall water splitting in acidic electrolyte was realized.On the other hand,the more active anodic oxidation reaction or electroflocculation reaction was used to replace the OER and optimized the water splitting composite system.The composite electrolysis cell could be driven at low voltage to realize hydrogen production and water purification.The main contents of this study are as following:?1?To overcome the problem of low activity and unstable electrocatalyst for cathode hydrogen production at large current density,we used the saccharomycete to adsorb precious metals ruthenium in water,then calcined to prepare Ru-Ru2P?NPC electrocatalyst with excellent HER performance.This process realized resource recovery and efficient HER electrocatalyst preparation at the same time.In the synthesis process of Ru-Ru2P?NPC,saccharomycete cells were not only acted as the carbon template,but also acted as biological phosphorus sources to realize in-situ solid-phase phosphation process.Theoretical calculations confirmed that the Ru-Ru2P heterojunction was conducive to improving the Gibbs free energy of hydrogen adsorption of the catalyst.The semi-embedded structure of the active material in Ru-Ru2P?NPC could fully expose the catalytic site and improve stability.The HER overpotential of Ru-Ru2P?NPC under acid electrolyte was only 42 m V at the current density of 10 m A/cm2,and it could be stably for 35 h at high current density?>1000m A/cm2?.In addition,using saccharomycete as the core template,NPC@Ru O2 as an excellent OER catalyst with yolk structure was synthesized.N/P co-doped carbon core could effectively improve the conductivity and stability of Ru O2 shell.Finally,an electrolytic cell?Ru-Ru2P?NPC?-?//NPC@Ru O2?+??was constructed to achieve overall water splitting,in which the voltage was only 1.5 V to reach the current density of 10 m A/cm2 in acid media.?2?Aiming at the slow kinetics of anode OER and the low economic value of oxygen production,we combined anodizing PMS to degrade organic pollutants with the cathodic HER to build a multifunctional composite electrolytic cell with water purification and hydrogen production.Using ZIF-67 as the precursor,a one-step calcination method was used to synthesize Co@N-C600 as bifunctional electrode materials to construct a composite electrolytic cell.It was found that the calcination temperature had an important effect on the performance of Co@N-C.When the calcination temperature was 600°C,the Co@N-C600showed the best performance for anode-activated PMS to degrade Orange II and cathode hydrogen production.When the Co@N-C600 anode coexisted with PMS,the removal rate of Orange?could reach 94.8%in 15 min under the working voltage of 2 V.For cathode HER,the initial potential is-51 m V@0.5 m A/cm2,and it had good stability for hydrogen production.Finally,the optimized composite electrolytic cell was applied with a voltage of 2 V to effectively remove Orange?pollutants with the flow rate of 50 m L/min in the anode chamber.At the same time,the H2 generation rate of 4.39 mmol/L in the cathode chamber could be achieved.?3?To further construct a composite electrolytic cell with low energy consumption and high energy efficiency,we used electroflocculation process to remove pollution as anode reaction to combine with cathode HER for anode water purification and cathode hydrogen production in a composite electrolytic cell.Using a“tip-growth”method,iron encapsulated in nitrogen-doped carbon nanotubes array?Fe@N-CNT?was synthesized and used as an effective electrode for HER.The unique three-dimensional array structure of Fe@N-CNT/IF was characterized by FESEM and TEM.The Fe@N-CNT/IF had excellent HER performance in 0.5 mol/L Na2SO4 electrolyte,with the overpotential of 525 m V@10 m A/cm2 as well as excellent stability.The flocculant produced in the electroflocculation process could effectively adsorb a variety of pollutants.A composite cell?Fe@N-CNT/IF?-?//?+?IF?was constructed for removal pollutants and hydrogen generation,which only needed a voltage of 1.31 V to reach the current density of 20 m A/cm2.Finally,we used a 1.5 V battery to drive the above composite electrolysis cell.The generation rate of H2 reached 4 m L/min,and the removal rate of the Rhodamine B reached 99.2%after the electrolysis cell operated for 10 min. |
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