| Hydrogen as green energy,which is recognized as a promising alternative to existing energy forms（e.g.,coal,petroleum,fossil fuels,etc.）for our society in the future.However,hydrogen production is still strongly dependent on limited fossil fuels that are finite and non-renewable resources.The preparation processes are complicated and the operation conditions are harsh,which consume lots of energy and the environment has been polluted seriously.Recently,the developed electrocatalytic and photoelectrocatalytic water splitting technology for sustainable hydrogen production has attracted much attention.However,the sluggish oxygen evolution reaction limits the cathode hydrogen production.Most research has been focused on designing the highly active and economical oxygen evolution reaction catalysts to decrease the anode overpotential for improved hydrogen production.It is known that some organic pollutants or biomass derivatives contain a lot of chemical energy,which is a good electron donor,and the oxidation potential is much lower than water.These thermodynamically more favorable reactions can replace water oxidation to achieve the effective removal of pollutants or the preparation of high value-added products and simultaneous hydrogen production,which has great environmental and energy significance.Hydrogen production by photoelectrocatalytic technology is still strongly limited by the slow anodic oxygen evolution reaction.In order to overcome the difficulty of the slow rate for hydrogen production,pollutants of phenol,biomass derivatives of benzyl alcohol,5-hydroxymethyl furfural,and tetrahydroisoquinoline are chosen as the model reaction to replace water oxidation for hydrogen production based on the aforementioned ideas.The relationship between anodic organic oxidation and cathodic hydrogen production is studied.The main conclusions from this work are listed as follows:（1）A rechargeable photoanode for organic pollutant phenol degradation to promote hydrogen productionA visible-light response dual-photoelectrodes solar-charged photoelectrochemical wastewater fuel cell（sc PEWFC）based on WO3 nanoflowers（NFs）-C/Cu2O nanowire array（NWAs）was constructed for efficient hydrogen production based on the promotion of phenol oxidation at the photoanode.It is of great practical significance to realize the efficient treatment of wastewater and alleviate the energy crisis to a certain extent.The hydrogen production reaches as high as 93.08μmol cm-2 by the photoelectrochemical oxidation of phenol（TOC removal rate reached 82.12%）of WO3NFs-C/Cu2O NWAs,which is 3.02 times higher than that of overall water splitting.It is found that sc PEWFC has excellent photoelectrochemical characteristics,and the VOCand JSC have reached 0.25 V and 0.47 m A cm-2,respectively.The photo-charging characteristics of WO3 and photoelectrochemical cell（PEC）were combined to construct a sc PEWFC,the hydrogen production(4 h,7.90μmol cm-2)was still carried out at the cathode under the dark owing to the stored electrons of WO3,which realized the ideal effect of full-day and high-efficiency hydrogen production.XRD,Raman and CV identified the mechanism of WO3 charging and discharging.The preparation conditions of WO3 NFs and the electrolyte concentration were optimized,and the performance parameters of sc PEWFC were also evaluated.The system shows good stability and recyclability after three cycles.（2）Photoelectrochemical cell for phenol degradation and simultaneous hydrogen production in a circulating flow deviceA photoelectrocatalytic interface of Mn Ox/Ti O2on a highly exposed（001）facet of single-crystal anatase Ti O2 was constructed,which realized the efficient removal of phenol and simultaneous hydrogen production.It was found that the addition of phenol effectively reduced the anode overpotential.Under 0.80 V（vs.Ag/Ag Cl）bias,the degradation rate of phenol in the Ti O2/Mn Ox photoanode>99%within 75 min,and the hydrogen production reached 244.5μmol cm-2.It was much higher than Ti O2(the degradation rate,73.2%,hydrogen production,185.3μmol cm-2).Such excellent performance can be attributed to the formation of p-n heterojunction,which promoted the separation of electrons and holes,and enhanced the photoelectrocatalytic conversion efficiency.In the phenol solution,the amount of hydrogen produced at the cathode was 8.4 times than that of pure water,indicating that phenol oxidation to replace water oxidation can promote hydrogen production.In addition,we have also found that batch processing of phenol was more conducive to hydrogen production.It was calculated that the contribution for phenol degradation of photoelectrocatalytic was much higher than the sum of photocatalytic（71.3%）and electrocatalytic（7.8%）,indicating that the electric field promoted the separation of electrons and holes and enhanced the photocatalytic conversion efficiency.Additionally,it was confirmed that hydroxyl radical was the main active species for phenol degradation by in-situ EPR.（3）Electrocatalytic selective conversion of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid to promote hydrogen productionThe bimetallic Ni Co2O4 electrode was constructed by hydrothermal method and>99%selectivity and Faradaic efficiency for the electrochemical selective conversion of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid（FDCA）under mild conditions was achieved for enhanced hydrogen production.Meanwhile,FDCA was also a high value-added product.It was found that the addition of 5-hydroxymethylfurfural（HMF）can significantly reduce the anode overpotential（220m V）and effectively increase the current density,so that the amount of hydrogen produced through coupling with HMF oxidation was 8.61 times higher compared with pure water splitting.The result indicated that the controllable selective oxidation of HMF to FDCA（thermodynamically and kinetically more favorable six electrons reaction）can completely replace OER（sluggish four electrons reaction）and synergistically promote hydrogen production.Operando electrochemical Raman confirmed that the main active species for selective electrochemical oxidation of HMF to FDCA is Ni OOH.EXAFS confirmed that the electric field induced the strain of Ni-O bonds to generate more Ni OOH in situ.The operando electrochemical infrared techniques and density functional theory（DFT）calculations further confirmed the reaction pathway of HMF to FDCA.（4）Electrocatalytic selective conversion of tetrahydroisoquinoline to dihydroisoquinoline to promote hydrogen productionBifunctional Co Fe-Ni Se2 electrode was designed and achieved almost>99%selective and Faradaic efficiency for selective conversion of tetrahydroisoquinolines（THIQs）to dihydroisoquinolines（DHIQs）and simultaneous hydrogen production（Faradaic efficiency 99.3%）under 1.45 V cell voltage.DHIQs were an important fine chemical that has great application prospects of bioactivities on anti-tumor,anti-fungal,vasodilation and nonoamine oxidase inhibition.It was found that the oxidation potential of THIQs was much lower than that of water,the addition of THIQs significantly reduces anode overpotential and enhances current density.The selective oxidation of THIQs to DHIQs and hydrogen production were integrated,so that the hydrogen production was 5.8 times higher than water splitting and the energy consumption was reduced by 11.2%.It showed that the oxidation of THIQs can completely replace water oxidation to achieve high efficiency hydrogen production at the cathode.It was confirmed that only primary oxidation of THIQs to DHIQs can promote hydrogen production.On the contrary,the deep oxidation of THIQs to IQs was not favorable to hydrogen production due to higher energy consumption.Operando Raman was used to detect the conversion of THIQs and the generation of DHIQs at different potentials.The main active species for selective conversion of THIQs was identified by XAFS.It was found that the co-doping of Co and Fe can promote the production of Ni OOH,to enhance the conversion of THIQs and simultaneous hydrogen production.（5）Photoelectrocatalytic selective conversion of benzyl alcohol to benzaldehyde to promote hydrogen productionA novel solar activated biomass photoelectrochemical cell（sa BPEC）was proposed for selective conversion of benzyl alcohol derivatives and simultaneous hydrogen production.It consists of a Bi2Mo O6@Ti O2 nanotube array（NTA）photoanode and C/Cu2O NW photocathode.The results showed that the sa BPEC has excellent photoelectrochemical performance.This primary oxidation of benzyl alcohol to benzaldehyde was realized with almost 100%selectivity,leading to promoted hydrogen production on a photocathode with an efficiency of 85%.The efficient conversion of benzyl alcohol can be attributed to the distribution of Lewis acids,which enhanced the adsorption of benzyl alcohol.At the same time,more Lewis basic sites were distributed on the surface of Bi2Mo O6,which can effectively adsorb and activate oxygen,to enhance the high selectivity of benzaldehyde.By introducing different substituents at the para position of benzyl alcohol,it was proved that the electron-donating group can promote the efficient conversion of benzyl alcohol.In addition,in the electrolyte containing benzyl alcohol,the amount of hydrogen was 5.5 times higher than that in pure water,which indicated that the controllable selective primary oxidation of benzyl alcohol to benzaldehyde could synergistically promote hydrogen production.The hydrogen production efficiency increased with the oxidation reaction rates.The operation mechanism and performance parameters of sa BPEC are thoroughly investigated. |
