Hybrid Micro/Nano-structures:Precise Synthesis And Their Multifunctional Electrocatalysis

The goal for peaking and neutralizing CO2 emission imposes the stringent strain on Energiewende.The electrocatalytic refinery（e-refinery）is a more sustainable and environmentally benign strategy to efficiently convert the abundant and renewable feedstocks to fuels and chemicals by renewable electricity,thus achieving the carbon-neutral and decentralized development.As the important "Strategy Energy",the scaling-up development of Green H₂ is still limited by the sluggish kinetics of the coupling water oxidation process,thus motivating the advanced design of high-efficient noble metal candidates as well as the smart energy-saving tactics for moving the bench-scale H₂ generation to commercial application.Focusing on this bullet point,this dissertation summarizes the electrocatalysis system for H₂ generation,such as the traditional water electrocatalysis and the hybrid water electrocatalysis,including hydrazine oxidation assisted H₂ generation and microbial electrocatalysis,then introduces the fundamental electrochemical reaction referred in these systems and the relevant electrocatalysts.Next,the electrocatalytic applications and the preparation of transition metal（phosphide）/carbon（TM（TMP）/C）hybrids have been reviewed,and the prospective of these materials on the multifunctional electrocatalysis has been pointed.In this dissertation,we rationally choose the low-cost while performance-developing TM（TMP）/C as the objects,precisely regulate the materials’electronic structure and carefully explore the atomic-level active sites,to realize the synergetic optimization of the materials’multifunctionality,thus achieving the energy-saving H₂ generation.The main research is showed as following:1.The strategy of polyol process and subsequent pyrolysis treatment has been developed to construct the hierarchical 3D macrosheets composed of interconnected in-situ cobalt catalyzed nitrogen doped carbon nanotubes（denoted as Co@NCNT HMS）.This Co/C hybrid exhibits excellent bifunctional oxygen activity with the potential gap of 0.681 V.Then,the home-made Zn-air battery with Co@NCNT HMS as the cathode can output the peak power density of 159.83 mW/cm2 and possesses the voltage retention of 97.3%during the long-term（175 h）charge-discharge cycle,thus providing the power for constructing the system of Air battery derived H₂ generation.2.To improve the poor HER activity of the above bifunctional Co/C electrocatalyst,the P element has been introduced.The safe and atoxic melamine phosphate as P source has been added in the supramolecular assembly of melamine and cyanuric acid,and the subsequent one-pot thermolysis further formed the unique donut-shaped hybrid nanostructure composed of interconnected CoP nanoparticles within P,N co-doped carbon matrix（denoted as CoP@PNC-DoS）,which integrates the multifunctional activity,including OER（η10=316 mV,1.0 M KOH）,ORR（E1/2=0.803 V,0.1 M KOH）,and HER（η10=173 mV,1.0 M KOH;η10=160 mV,0.5 M H₂SO4）,as well as the enhanced stability.This CoP@PNC-DoS composite also holds the good bifunctional oxygen performance（△E=0.781 V,0.1 M KOH）and the OWS capacity（E10=1.74 V,1.0 M KOH）.Also,the resultant product can be used as the cathode of the home-made Zn-air battery,which has the dominant power density of 138.57 mW/cm2 and the remarkable charge-discharge stability（175 h）under the large current density of 30 mA cm-2.Further,the "Air-driven" H₂ generation has been demonstrated through the integrated system of the Zn-air battery powered water electrolysis with this hybrid as the only electrocatalyst.3.Induced by the above phosphorization tactics,the facile and scalable strategy of simple adsorption and one-pot thermolysis has been developed to precisely synthesize the partially exposed RuP₂ nanoparticle decorated N,P dual-doped carbon porous microsheets（denoted as RP-CPM）,whose activities outperform benchmark Pt/C toward both HzOR and HER in alkaline condition.Specifically,it only requires an ultrasmall working potential of-70 mV to reach 10 mA/cm2 for HzOR and an extremely low overpotential of 24 mV at 10 mA/cm2 for HER.Outstandingly,a record-low cell voltage of 23 mV is needed to obtain the same current density in a two-electrode system for OHzS,much smaller than the corresponding OWS（2.349 V）,and an industry-level current density of 522 mA cm-2 can be reached at a small cell voltage of 1.0 V,thus exhibiting the bright prospect for energy-saving H₂ generation.The DFT calculations combined with the experimental results decipher that the active Ru sites in the hybrid structure have more favorable kinetics for N2H4 adsorption and the subsequent dehydrogenation of the intermediates,and the C sites near the interface exhibit more thermoneutral hydrogen absorption for HER,demonstrating the significance of the partially exposed RuP₂ surface for the improved bifunctionality.4.The above RuP₂/C composite（denoted as RP-HNS in this chapter）further possesses the marvelous HER performance in neutral condition with the smaller overpotential of 26 mV than the state-of-the-art Pt/C（27 mV）at 10 mA cm-2 and the long-time durability（110 h）.When assembling the cathodic RP-HNS in the single-chamber MEC,this electrochemical system can evolve H₂ at merely 0.18 V,and offers the high current density of 10 A/m2 at 0.64 V,100 mV smaller than the comparing Pt/C（0.74 V）,suggesting this hybrid can be used as the Pt candidate for the energy-saving H₂ generation via MEC.