Synthesis And Evaluation Of Noble Metal Free Catalysts For Photo/Electrochemical Nitrogen Reduction To Ammonia Under Ambient Conditions

The efficient energy conversion technologies with outstanding sustainability are highly desired worldwide to fulfil the ever-increasing energy demand during the past few decades.Recently,electrochemical nitrogen(N2)reduction to ammonia(NH3)is an intriguing strategy for effective nitrogen utilization but still suffering low Faraday efficiency and NH3 yields.NH3 is playing a significant role in fertilizer production to support the human population on planet,served as a renewable energy carrier as well as zero-carbon emission fuel.Currently,it is produced by eco-unfriendly and high energy-intensive"Haber-Bosch" process.Amongst the available alternatives for NH3 synthesis,electrochemical nitrogen reduction reaction(NRR)at ambient conditions grasped attention due to compact and on-site electrolytic cells that can operate through solar or wind powers.Based on successful design strategies and catalytical performances,various recently identified NRR electrocatalysts such as metal carbides,nitrides,oxides,phosphides,sulfides,selenides,composites,metalorganic frameworks,bimetallic and metal-free materials are summarized by focusing on the theoretical analysis and experimental investigations collectively.Therefore,the aim of this work is to design and explore the efficient,selective and low-cost photo/electrocatalytic materials for ambient N2 reduction to NH3 with high stability and catalytic performance.Ammonia is a vital chemical and primary contributor to fertilizers,hydrogen,and modern renewable fuel generation.The prepared MoSe2@g-C3N4 hybrid heterostructures are capable to serve as catalysts for photoelectrochemical(PEC)N2 reduction to NH3 at relatively low potential(-0.3 V vs.RHE)in 0.1 M KOH solution at environmental conditions.The in-situ fabrication of hierarchical MoSe2 micro/nanoflowers with exfoliated nanosheets of g-C3N4 greatly improved the Faradaic efficiency(FE)and NH3 yield up to 28.91%and 131.47 μg h-1 mgcat-1(7.72 μmol h-1 cm-2),respectively.The improved PEC catalytic performance might be accredited to hierarchical micro/nanoarchitecture,light-harvesting ability,heterojunctions formation,abundant and tunable catalytic sites,as verified by density functional theory(DFT)calculations as well as several characterization techniques.Therefore,this study not only provides an efficient means of obtaining hierarchical heterostructure materials for effective PEC N2 reduction but also offers a profound insight into N2 reduction using MoSe2@g-C3N4 hybrids.The photoelectrochemical fixation of atmospheric N2 into valuable chemicals is a favorable strategy to utilize the available abundant natural resources by exploring efficient catalyst systems.It is extremely desirable to discover inexpensive,immensely active,durable,and selective materials for effective photoelectrochemical nitrogen fixation.We also synthesized the lowcost,non-noble metal-based porous Mo-doped WO3@CdS hierarchical hollow microspheres heterostructures that can effectively catalyze and reduce the gaseous nitrogen into ammonia.A high Faradaic efficiency(36.72%)and average ammonia yield rate(38.99 μg h-1 mgcat-1)were observed at-0.3 V vs.RHE in the neutral solution at environmental conditions.Molybdenum doping and interconnected porous heterostructures network deliver sufficient catalytic sites for effective nitrogen reduction during the photoelectrocatalytic NRR.The robust architecture of Mo-WO3@CdS enable the rapid charge/mass transport rate due to hollow and porous conductive network formation between doped WO3 and CdS nanoparticles.This innovative architecture might facilitate the better contacts between Mo-doped WO3 hollow spheres and CdS nanoparticles.Therefore,the present work demonstrates the substantial rational construction strategy of transition metals-based hierarchical hollow photoelectrocatalysts towards impending nitrogen fixation.Innovative advances in the exploitation of effective electrocatalytic systems for N2 to NH3 reduction are highly required for the sustainable production of fertilizers and zero-carbon emission fuel.In order to achieve low-carbon and renewable NH3 production,electrochemical NRR provide a favorable energysaving alternative but it still requires more active,efficient,and selective catalysts.Keeping in view,the aim to design and explore the electrocatalytic N2 reduction performance of multi-component systems,we synthesized the NiCo2S4@MnO2 heterostructure.The NiCo2S4@MnO2 heterostructures are efficaciously fabricated via a facile hydrothermal approach.The X-ray photoelectron spectroscopy(XPS)and scanning electron microscopy(SEM)demonstrated that the nanoflakes of MnO2 are consistently curled across the surface of NiCo2S4 nanoneedles and forming core-shell heterostructure that incorporates the benefits of both NiCo2S4 and MnO2.The urchin-like NiCo2S4@MnO2 heterostructures serve as cathode material and demonstrated a high NH3 yield of 57.31 μg h-1 mgcat-1 and FE of 20.55%at-0.2 V vs.RHE in basic electrolyte owing to the synergistic interactions of NiCo2S4 and MnO2.These distinctive nano-architectures exhibit high NRR electrocatalytic activities that might motivate researchers to further explore and concentrate on the development of heterostructure materials for ambient electrochemical ammonia synthesis.