Engineering the morphology and electronic structure of atomic cobalt-nitrogen-carbon catalyst with highly accessible active sites for enhanced oxygen reduction

The stabilization of non-precious metals as isolated active sites with high loading density over nitrogendoped carbon materials is essential for realizing the industrial application of single atom catalysts.However,achieving high loading of single cobalt active sites with greatly enhanced oxygen reduction reaction(ORR)activity and stability remains challenging.Here,an efficient approach was described to create a single atom cobalt electrocatalyst(Co SAs/NC)which possesses enhanced mesoporosity and specific surface area that greatly favor the mass transportation and exposure of accessible active sites.The electronic structure of the catalyst by the strong metal-support interaction has been elucidated through experimental characterizations and theoretical calculations.Due to dramatically enhanced mass transport and electron transfer endowed by morphology and electronic structure engineering,Co SAs/NC exhibits remarkable ORR performance with excellent activity(onset and half-wave potentials of 1.04 V(RHE)and 0.90 V(RHE),Tafel slope of 69.8 mV dec^(-1)and J_(k) of 18.8 mA cm^(-2)at 0.85 V)and stability(7 mV activity decay after 10,000 cycles).In additio n,the catalyst demonstrates great promise as an alternative to traditional Pt/C catalyst in zinc-air batteries while maintaining high performance in terms of high specific capacity of(796.1 mAh/g_(Zn)),power density(175.4 mW/cm^(2)),and long-term cycling stability(140 h).This study presents a facile approach to design SACs with highly accessible active sites for electrochemical transformations.

Emerging strategies and developments in oxygen reduction reaction using high-performance platinum-based electrocatalysts

The global practical implementation of proton exchange membrane fuel cells(PEMFCs)heavily relies on the advancement of highly effective platinum(Pt)-based electrocatalysts for the oxygen reduction reaction(ORR).To achieve high ORR performance,electrocatalysts with highly accessible reactive surfaces are needed to promote the uncovering of active positions for easy mass transportation.In this critical review,we introduce different approaches for the emerging development of effective ORR electrocatalysts,which offer high activity and durability.The strategies,including morphological engineering,geometric configuration modification via supporting materials,alloys regulation,core-shell,and confinement engineering of single atom electrocatalysts(SAEs),are discussed in line with the goals and requirements of ORR performance enhancement.We review the ongoing development of Pt electrocatalysts based on the syntheses,nanoarchitecture,electrochemical performances,and stability.We eventually explore the obstacles and research directions on further developing more effective electrocatalysts.

Total conversion of centimeter-scale nickel foam into single atom electrocatalysts with highly selective CO_(2)electrocatalytic reduction in neutral electrolyte

To improve the atomic utilization of metals and reduce the cost of industrialization,the one-step total monoatomization of macroscopic bulk metals,as opposed to nanoscale metals,is effective.In this study,we used a thermal diffusion method to directly convert commercial centimeter-scale Ni foam to porous Ni single-atom-loaded carbon nanotubes(CNTs).As expected,owing to the coating of single-atom on porous,highly conductive CNT carriers,Ni single-atom electrocatalysts(Ni-SACs)exhibit extremely high activity and selectivity in CO_(2)electroreduction(CO_(2)RR),yielding a current density of>350 mA/cm^(2),a selectivity for CO of>91%under a flow cell configuration using a 1 M potassium chloride(KCl)electrolyte.Based on the superior activity of the Ni-SACs electrocatalyst,an integrated gas-phase electrochemical zero-gap reactor was introduced to generate a significant amount of CO current for potential practical applications.The overall current can be increased to 800 mA,while maintaining CO Faradaic efficiencies(FEs)at above 90%per unit cell.Our findings and insights on the active site transformation mechanism for macroscopic bulk Ni foam conversion into single atoms can inform the design of highly active single-atom catalysts used in industrial CO_(2)RR systems.

Single-atom electrocatalyst and gel polymer electrolyte boost the energy density and life of aluminum-sulfur batteries

Aluminum-sulfur(Al-S)batteries are regarded as a desirable candidate for large-scale energy storage be-cause of their high energy density and abundant natural resources of electrode materials.To address the critical issues of low discharge voltage and rapid capacity decay in Al-S batteries,here an electrocatalyst-assisted gel-polymer electrolyte(GPE)-based Al-S battery is fabricated using platinum nanoparticles deco-rated platinum/nitrogen co-doped graphene(PtNG)as sulfur host for positive electrode and metal-organic frameworks(MOF)filled GPE(MOF@GPE)as solid electrolyte.Pt-based active sites derived from Pt nan-oclusters’surface and atomically dispersed Pt-N_(2) chemical bonds in PtNG can catalyze the decomposition of sulfur and polysulfides in the electrochemical process,greatly accelerating the sulfur redox kinetics.Furthermore,the MOF fillers in MOF@GPE electrolyte significantly inhibit the shuttle effect of polysul-fides,efficiently improving the utilization of sulfur.Consequently,the established Al-S battery delivers a specific capacity of 1009 mAh g^(−1) with a discharge plateau of∼0.95 V,along with a capacity retention of 65% after 300 cycles,revealing ultrahigh energy density and long cycle life.Such a strategy of combin-ing electrocatalyst and MOF-based gel electrolyte affords a fresh plateau for promoting the rechargeable ability of Al-S batteries,advancing remarkable routes for achieving efficient and stable energy storage devices.

Enhancing electrical conductivity of single-atom doped Co_(3)O_(4) nanosheet arrays at grain boundary by phosphor doping strategy for efficient water splitting

High electrical conductivity guarantees a rapid electron transfer and thus plays an important role in electrocatalysis.In particular,for the single atom catalysts(SACs),to facilitate interaction between the single atom and supports,precisely engineering the conductivity represents a promising strategy to design SACs with high electrochemical efficiency.Here we show rhodium(Rh)SAC anchored on Co_(3)O_(4) nanosheets arrays on nickel foam(NF),which is modified by a facile phosphorus(P-doped Rh SACCo_(3)O_(4)/NF),possessing an appropriate electronic structure and high conductivity for electrocatalytic reaction.With the introduction of P atom in the lattice,the electrocatalyst demonstrates outstanding alkaline oxygen evolution reaction(OER)activity with 50 mA·cm^(−2) under overpotential of 268 mV,6 times higher than that of Ir/C/NF.More interestingly,the P-doped Rh SAC-Co_(3)O_(4)/NF can get 50 mA·cm^(−2) at only 1.77 V for overall water splitting.Both electrical conductivity studies and density functional theory(DFT)calculations reveal that the high conductivity at grain boundary improves the charge transfer efficiency of the Rh catalytic center.Furthermore,other noble-metal(Ir,Pd,and Ru)doped Co_(3)O_(4) nanosheets arrays are prepared to exhibit the general efficacy of the phosphorus doping strategy.