Selective sulfur conversion with surface engineering of electrocatalysts in a lithium-sulfur battery

The sluggish kinetics of multiphase sulfur conversion with homogeneous and heterogeneous electrochemical processes,causing the“shuttle effect”of soluble polysulfide species(PSs),is the challenges in terms of lithium-sulfur batteries(LSBs).In this paper,a Mn_(3)O_(4-x) catalyst,which has much higher activity for heterogeneous reactions than for homogeneous reactions(namely,preferentialactivity catalysts),is designed by surface engineering with rational oxygen vacancies.Due to the rational design of the electronic structure,the Mn_(3)O_(4-x) catalyst prefers to accelerate the conversion of Li2S4 into Li_(2)S_(2)/Li_(2)S and optimize Li_(2)S deposition,reducing the accumulation of PSs and thus suppressing the“shuttle effect.”Both density functional theory calculations and in situ X-ray diffraction measurements are used to probe the catalytic mechanism and identify the reaction intermediates of MnS and Li_(y)Mn_(z)O_(4-x) for fundamental understanding.The cell with Mn_(3)O_(4-x) delivers an ultralow attenuation rate of 0.028% per cycle over 2000 cycles at 2.5 C.Even with sulfur loadings of 4.93 and 7.10mg cm^(-2) in a lean electrolyte(8.4μL mg s^(-1)),the cell still shows an initial areal capacity of 7.3mAh cm^(-2).This study may provide a new way to develop preferential-activity heterogeneous-reaction catalysts to suppress the“shuttle effect”of the soluble PSs generated during the redox process of LSBs.

Facile carbon cloth activation strategy to boost oxygen reduction reaction performance for flexible zinc-air battery application

Flexible and all-solid-state zinc-air batteries(ZABs)are highly useful and also in demand due to their theoretical high energy densities and special applications.The limitation in their performance arises due to their catalyst-coated cathode electrodes in terms of catalytic activity and stability as well as cost.In this paper,a novel and environmentally friendly activation strategy is developed to activate the carbon cloth(CC)for the electrodes.The activated CC serves as a catalyst-free air cathode with high conductivity,excellent mechanical strength,and flexibility,in addition to low cost.The strategy is performed by simply electro-oxidizing and electroreducing CC under ultrahigh direct current(DC)voltage in a diluted NH4Cl aqueous electrolyte.It is found that the electro-oxidation not only results in the formation of a graphene-like exfoliated carbon layer on the surface of CC but also induces the incorporation of oxygen-containing groups and doping of nitrogen and chloride atoms.After the electroreduction,theπ-conjugated carbon network of CC is partially restored,leading to the recovery of electroconductivity.Such an electroactivated CC shows excellent oxygen reduction reaction activity.The aqueous flexibility and all-solid-state ZABs are assembled using such an electroactivated CC cathode without any catalyst loading.Both ZABs can achieve good durability and deliver high peak power density and an energy density as high as 690 Wh kg^(−1),demonstrating the excellent potential of this electroactivated CC in practical devices.

Pd nanocluster-decorated CoFe composite supported on nitrogen carbon nanotubes as a high-performance trifunctional electrocatalyst

Rational design and synthesis of low-cost trifunctional electrocatalysts with improved stability and superior electrocatalytic activity for oxygen reduction reaction(ORR),oxygen evolution reaction(OER),and hydrogen evolution reaction(HER) are highly desirable but remain as the bottlenecks at the current state of technology.In this paper,the cobalt-iron(Co-Fe) composite supported on nitrogen-doped carbon nanotubes(CoFe composite/NCNTs) is synthesized.The intrinsic OER and HER catalytic activities of this CoFe composite/NCNTs composite are significantly improved with palladium(Pd) nanocluster decoration [Pd-coated(CoFe composite/NCNTs)].The as-prepared Pd-coated(CoFe composite/NCNTs) catalyst exhibits excellent trifunctional electrocatalytic activity and stability due to the interfacial coupling between Pd and(CoFe composite/NCNTs).This catalyst is successfully employed in the water electrolysis cell as both OER and HER electrode catalysts,flexible rechargeable Zn-air battery as the bifunctional ORR and OER electrode catalyst.The cell voltage of this catalyst-coated electrodes requires only 1.60 V to achieve 10 mA cm^(-2) current density for water electrolysis cell,which is comparable to and even better than that of Pt/C and Ir/C based cell.The primary Zn-air battery using this catalyst shows a constant high open-circuit voltage(OCV) of 1.47 V and a maximum power density of 261 mW cm^(-2) in the flooded mode configuration.Most importantly,a flexible Zn-air battery with this catalyst runs very smoothly without a change in voltage gap during flat,bending,and twisting positions.