While the sulfur conversion reaction kinetics in Li–S batteries is nowadays improved by the use of appropriate electrocatalysts,it remains a challenge for the batteries to perform well under the lean electrolyte cond...While the sulfur conversion reaction kinetics in Li–S batteries is nowadays improved by the use of appropriate electrocatalysts,it remains a challenge for the batteries to perform well under the lean electrolyte condition where polysulfide shuttle,electrode passivation and the loss of electrolyte due to side reactions,are aggravated.These challenges are addressed in this study by the tandem use of a polysulfide conversion catalyst and a redox–targeting mediator in a gel sulfur cathode.Specifically,the gel cathode reduces the polysulfide mobility and hence the polysulfide shuttle and the passivation of the lithium anode by the crossover polysulfides.The redox mediator restrains the deposition of inactive sulfur species in the cathode thereby enabling the Fe–N and Co–N co–doped carbon catalyst to prolong its catalytic activity.Consequently,the integrated catalytic system is able to increase the discharge capacity of high–loading (6.8 mg cm^(-2)) lean–electrolyte (4.0μL mg^(-1)) Li–S batteries from~630 to~1316 m Ah g^(-1),concurrently with an improvement of the cycle life (600 cycles with 46%capacity retention at 1.0 m A cm^(-2)).Redox mediator assisted catalysis in a gel cathode is therefore an effective strategy to extend the application of the sulfur conversion catalyst in lean electrolyte Li–S batteries.展开更多
The oxygen evolution reaction(OER)in acid solution is a significant challenge for non-precious metal electrocatalysts based on the transition metals although they have shown good OER performance in alkaline solution.I...The oxygen evolution reaction(OER)in acid solution is a significant challenge for non-precious metal electrocatalysts based on the transition metals although they have shown good OER performance in alkaline solution.In this study,we synthesized the electrocatalysts containing two or three Co species(Co,CoO and Co3O4)nanoparticles on porous graphitic carbon(PGC)nanosheets which were prepared by a facile and low-cost synthesis where Co(NO3)2•6H2O and glucose were pyrolyzed in the presence of sodium chloride template.The Co3O4-dominated catalyst as-prepared,Co3O4/PGC,is OER active in acid solution(1.74 V at a current density of 10 mA cm^−2).We identified the OER active sites in the catalyst to be the Co3O4 nanoparticles rather than carbon-coated Co.Through comparative studies of the varied catalysts,we also proved that Co3O4 is catalytically more active than Co and CoO.The Co3O4/PGC catalyst,however,lost almost of all its activity after 100 voltammetric cycles in the 1.2-1.8 V voltage window.When the catalyst stability was examined potentiostatically at different potentials,the catalyst showed good stability at 1.4 V.The stability study also revealed the mechanism of the catalyst instability in acid was caused by Co3O4 reduction below 1.4 V and by Co3O4 oxidation above 1.4 V.1.4 V is therefore a unique potential where Co3O4 nanoparticles are neither oxidized nor reduced to be susceptible to acid dissolution.展开更多
Recent years have seen a significant surge in energy storage research and development across the globe. This is due to a number of factors including the increasingly grave environmental concerns, increased energy cons...Recent years have seen a significant surge in energy storage research and development across the globe. This is due to a number of factors including the increasingly grave environmental concerns, increased energy consumption, rising fuel prices, limited fossil fuel resources and the growing interest in the expansion of renewable energy utilization. Energy exists in different forms including electrical, magnetic, mechanical, chemical and thermal energy. These forms of energy have different grades with electrical energy being the highest and thermal energy the lowest. Energy storage refers to a process whereby excess energy is stored in a form that can be converted back to the same form or into a different form when needed.展开更多
基金the financial support provided by the National University of Singapore。
文摘While the sulfur conversion reaction kinetics in Li–S batteries is nowadays improved by the use of appropriate electrocatalysts,it remains a challenge for the batteries to perform well under the lean electrolyte condition where polysulfide shuttle,electrode passivation and the loss of electrolyte due to side reactions,are aggravated.These challenges are addressed in this study by the tandem use of a polysulfide conversion catalyst and a redox–targeting mediator in a gel sulfur cathode.Specifically,the gel cathode reduces the polysulfide mobility and hence the polysulfide shuttle and the passivation of the lithium anode by the crossover polysulfides.The redox mediator restrains the deposition of inactive sulfur species in the cathode thereby enabling the Fe–N and Co–N co–doped carbon catalyst to prolong its catalytic activity.Consequently,the integrated catalytic system is able to increase the discharge capacity of high–loading (6.8 mg cm^(-2)) lean–electrolyte (4.0μL mg^(-1)) Li–S batteries from~630 to~1316 m Ah g^(-1),concurrently with an improvement of the cycle life (600 cycles with 46%capacity retention at 1.0 m A cm^(-2)).Redox mediator assisted catalysis in a gel cathode is therefore an effective strategy to extend the application of the sulfur conversion catalyst in lean electrolyte Li–S batteries.
基金supported by the National Research Foundation,Prime Minister’s Office,Singapore under its Competitive。
文摘The oxygen evolution reaction(OER)in acid solution is a significant challenge for non-precious metal electrocatalysts based on the transition metals although they have shown good OER performance in alkaline solution.In this study,we synthesized the electrocatalysts containing two or three Co species(Co,CoO and Co3O4)nanoparticles on porous graphitic carbon(PGC)nanosheets which were prepared by a facile and low-cost synthesis where Co(NO3)2•6H2O and glucose were pyrolyzed in the presence of sodium chloride template.The Co3O4-dominated catalyst as-prepared,Co3O4/PGC,is OER active in acid solution(1.74 V at a current density of 10 mA cm^−2).We identified the OER active sites in the catalyst to be the Co3O4 nanoparticles rather than carbon-coated Co.Through comparative studies of the varied catalysts,we also proved that Co3O4 is catalytically more active than Co and CoO.The Co3O4/PGC catalyst,however,lost almost of all its activity after 100 voltammetric cycles in the 1.2-1.8 V voltage window.When the catalyst stability was examined potentiostatically at different potentials,the catalyst showed good stability at 1.4 V.The stability study also revealed the mechanism of the catalyst instability in acid was caused by Co3O4 reduction below 1.4 V and by Co3O4 oxidation above 1.4 V.1.4 V is therefore a unique potential where Co3O4 nanoparticles are neither oxidized nor reduced to be susceptible to acid dissolution.
文摘Recent years have seen a significant surge in energy storage research and development across the globe. This is due to a number of factors including the increasingly grave environmental concerns, increased energy consumption, rising fuel prices, limited fossil fuel resources and the growing interest in the expansion of renewable energy utilization. Energy exists in different forms including electrical, magnetic, mechanical, chemical and thermal energy. These forms of energy have different grades with electrical energy being the highest and thermal energy the lowest. Energy storage refers to a process whereby excess energy is stored in a form that can be converted back to the same form or into a different form when needed.
