Ni,Co Based Nanostructure Materials For Energy Conversion And Storage Applications

Worldwide energy demands are escalating dramatically owing to changes of the lifestyles and the rising of population.The primary resources of global energy in the entire history are fossil fuels.However,the limited resource of fossil fuel is a severe concern.In coincidence with the non-renewable nature and increasingly restricted simple accessibility,numerous guesstimates have concluded that our reserves may be exhausted in as few as 100 years based on present utilization trends,and,ultimately,one day it will be finished.Furthermore,environmental issues are also more severe,which generated due to burning of fossil fuels.Thus,it is essential and urgent to search sustainable energy alternatives option,together with both green energy sources and energy storage systems.There are several renewable and green energy systems such as:Supercapacitors,Li-batteries(LIBs),Na-batteries(NIBs),K-batteries(KIBs),metal air-batteries(MABs),fuel cells and solar cells etc,which have acknowledged a lot of industrial achievements.However,several issues influence the effectiveness of energy systems(i.e.percentage yield,the ratio between generated electricity and input energy).Therefore,the most important challenge in the success of any renewable energy technology is to maximize its efficiency and it is mainly reliant on the structure and properties of candidate materials.Electrochemical energy conversion and storage devices can be classified into batteries,capacitors and water splitting due to their different working principles.Two-dimensional(2D)nanomaterials with high specific surface area and mesoporous nature are attractive and have wide applications in catalysis and energy storage systems etc.Here,we report a novel strategy to fabricate noble metal-free,F-doped ?-Ni(OH)2 mesoporous 2D ultrathin nanosheets.The F-doped Ca-Ni(OH)2 nanosheets exhibit remarkable electrocatalytic activity and stability for oxygen evolution reaction,achieving low onset potential(260 mV),high mass activity(69.1 A g-1 at ?=350 mV)and low tafel slop(31.89 mV dec-1),which is superior than commercial RuO2 catalysts.Simultaneously,F-doped ?-Ni(OH)2 nanosheets are found to have high specific capacitance of 158.75 F g-1 at 1 A g-1 with maximum energy density of 67.4 Wh kg-1 at power density of 400 W kg-1,which could still retain 40 Wh kg-1 at power density of 16 kW kg-1.DFT calculation rationalizes that F doping ?-Ni(OH)2 favors electrical conductivity,efficient electron transport and water adsorption.It could be envisioned that the proposed simple and efficient approach will pave a new way to synthesize other anions doped 2D materials for energy conversion and storage technology.Due to promising electrode performance in energy storage devices,Sodium metal fluorides(NaMF3,M= Fe,Ni,Co,etc)are attracting considerable attention of researchers.These fluorides usually synthesized by using binary fluorides at high temperature(700?-900?),which is difficult and expensive way.Therefore,easy and cheaper ways are essential to prepare these perovskite fluorides to achieve better performance.Here,we have synthesized perovskite fluoride(NaNiF3)hollow spheres via a simple and cost effective approach and described the formation mechanism of hollow spheres,which was recrystallization accompanied by morphology and phase change process and also applied as a novel and potential electrode material for supercapacitors,which exhibited high specific capacitance(1342 F g-1 at 5 A g-1),excellent rate performance and long cycle stability(more than 90%capacity retention after 8,000 cycles).When they were coupled with activated carbon electrode,NaNiF3//AC asymmetric device displayed a wide voltage window(1.65 V)and exhibited maximum energy density(51.78 Wh kg-1 at power density of 1.65 kW kg-1)with excellent cyclic stability(100%capacity retention from 1400 to 10,000 cycles).It could be envisioned that the proposed simple and efficient approach will pave a new way to synthesize and explore new perovskite fluorides with high performance for energy conversion and storage.Potassium-ion batteries(KIBs)are attractive as a promising alternative to lithium-ion batteries(LIBs)due to the low-cost and earth-abundant potassium resources.However,the lack of suitable materials for the intercalation/deintercalation of large-sized potassium ions is a major challenge.Here,we report nickel selenide nanoparticles with an average size of 25-40 nm encapsulated in nitrogen-doped carbon(NSC)as an advanced anode for KIBs.Benefiting from the unique structure,the intrinsic properties of metal-selenium bonds and a remarkable pseudocapacitance effect,the anode exhibits a very high reversible capacity of 438 mAh g-1 at 50 mA g-1,an excellent rate capability of 150 mA h g-1 at 5000 mA g-1 and remarkable cycling performance over 2000 cycles at 2000 mA g-1.In-situ X-ray diffraction,ex-situ high-resolution transmission electron microscopy and SAED techniques were used to investigate the potassiation/depotassiation mechanism.By coupling NSC as the anode and Prussian blue as the cathode,a reversible capacity of 204 mA h g-1 at 200 mA g-1 is obtained in a full-cell configuration.We envisage that the simple and efficient approach proposed here will provide a new emphasis on seeking for advanced anode materials for KIBsCo0.85Se hollow spheres that are constructed with 2D mesoporous ultrathin nanosheets were synthesized via simple and cost effective approach.Bifunctional electrocatalytic-supercapacitive properties are obtained simultaneously due to synergistic effects between macroscopic morphological features and microscopic atomic/electronic structure of Co0.85Se.The as-synthesized Co0.85Se hollow spheres constructed with 2D mesoporous ultrathin nanosheets exhibit inspiring electrochemical performance for supercapacitor,presenting maximum energy density at high power density(54.66 Wh kg-1 at 1.6 kW kg-1)and long cycle stability(88%retention after 8000 cycles).At the same time,the Co0.85Se hollow spheres constructed with 2D mesoporous ultrathin nanosheets display excellent catalytic performance for OER due to special structure,high surface area and mesoporous nature of sheets,which achieving low overpotential(290 mV)and low Tafel slope(81 mV dec-1)for long-term operation(only 7.8%decay in current density after 9 h).It could be envisioned that the proposed simple approach will pave a new way to synthesize other metal chalcogenides for energy conversion and storage technology.