A global priority is the development of low-cost, efficient storage of off-peak electric power and of electrical energy generated by energy sources other than fossil fuels (e.g. wind, solar, nuclear).[1] The rechargeable battery offers efficient electrical energy storage (EES), but the Li-ion battery used in hand-held devices is too expensive for large-scale EES. Unlike Li, Na is readily available worldwide and therefore much less costly than Li. However, the existing Na/S [2] and Zebra (Na/NiCl 2 ) [3] batteries are operating on molten electrodes at 250 to 350 8C. Therefore, there is a huge incentive to develop a room-temperature rechargeable, low-cost Na-ion battery (SIB) of high energy density capable of discharge/ charge at a high rate.To date, room-temperature rechargeable batteries have used as cathode oxide hosts into/from which the working ion, H + or Li + , can be inserted/extracted reversibly over a limited solid-solution range. These two working ions are able to be mobile guests in a host having a close-packed oxide-ion array. However, Na + is too large to be sufficiently mobile in a host with close-packed oxide ions; it needs a host framework with a larger interstitial space. Although Na + is stable coordinated by 12 oxide ions in an oxoperovskite, for example, the Na x WO 3 bronze, too high an activation energy is required for Na + transfer between these sites across a shared face coordinated by four oxide ions. The O-2p orbitals that s bond to the Na impede its motion. Replacement of the O 2À ions by (C N) À ions weakens bonding to the Na; the activation energy for Na + transfer is, therefore, strongly reduced, which makes attractive exploration of hexacyanoperovskites as cathode hosts for a rechargeable SIB. We report a synthesis route for a sodium manganese hexacyanoferrate (NMHFC) containing low-cost cations, and we demonstrate that the NMHFC provides a promising highrate performance as the cathode of a SIB of high specific energy density and efficient EES.Prussian blue and its analogues were investigated as hosts for alkali ions several years ago, [4] but that work received little attention. Cui and co-workers have recently reported stable Na + cyclability into potassium copper hexacyanoferrate in an aqueous electrolyte, [5] but an aqueous electrolyte limits the stable voltage of a rechargeable battery to 1.5 V. Therefore, we have chosen to investigate the hexacyano-perovskites in a non-aqueous electrolyte. We have reported the activities versus Na + /Na 0 of KMFe(CN) 6 with M = Fe, Co, Ni, Mn, Zn; high-spin M = Mn II showed a reversible plateau at 3.82 and 3.56 V, [6] respectively, on charge and discharge. We report herein removal of the Na + ion for a SIB to obtain a 3.4 V cathode in a Na half-cell with rhombohedral Na 1.72 MnFe(CN) 6 (NMHFC-1) and compare the performance with that of a cubic Na 1.40 MnFe(CN) 6 (NMHFC-2).The molar Na:Fe:Mn ratios of the sodium manganese hexacyanoferrates were obtained by inductively coupled plasma (ICP) analysis. All the metal atoms were normalized to the Mn c...

Transition-metal phosphides (TMPs) have emerged as promising catalyst candidates for the hydrogen evolution reaction (HER). Although numerous methods have been investigated to obtain TMPs, most rely on traditional synthetic methods that produce materials that are inherently deficient with respect to electrical conductivity. An electrospinning-based reduction approach is presented, which generates nickel phosphide nanoparticles in N-doped porous carbon nanofibers (Ni P@NPCNFs) in situ. Ni P nanoparticles are protected from irreversible fusion and aggregation in subsequent high-temperature pyrolysis. The resistivity of Ni P@NPCNFs (5.34 Ω cm) is greatly decreased by 10 times compared to Ni P (>10 Ω cm) because N-doped carbon NFs are incorporated. As an electrocatalyst for HER, Ni P@NPCNFs reveal remarkable performance compared to other previously reported catalysts in acidic media. Additionally, it offers excellent catalytic ability and durability in both neutral and basic media. Encouraged by the excellent electrocatalytic performance of Ni P@NPCNFs, a series of pea-like M P@NPCNFs, including Fe P@NPCNFs, Co P@NPCNFs, and Cu P@NPCNFs, were synthesized by the same method. Detailed characterization suggests that the newly developed method could render combinations of ultrafine metal phosphides with porous carbon accessible; thereby, extending opportunities in electrocatalytic applications.

No abstract

The practical application of lithium-sulfur (Li-S) batteries remains remote because of rapid capacity fade caused by the low conductivity of sulfur, dissolution of intermediate lithium polysulfides, severe volumetric expansion, and slow redox kinetics of polysulfide intermediates. Here, to address these obstacles, a new sulfiphilic and highly conductive honeycomb-like spherical cathode host constructed from hollow metallic and polar Co 9 S 8 tubes is designed. Co 9 S 8 can effectively bind polar polysulfides for prolonged cycle life, due to the strong chemisorptive capability for immobilizing the polysulfide species. The hollow structure, as the sulfur host, can further prevent polysulfide dissolution and offer sufficient space to accommodate the necessary volume expansion. Well-aligned tubular arrays provide a conduit for rapid conduction of electrons and Li-ions. More importantly, the experimental results and theoretical calculations show that Co 9 S 8 plays an important catalytic role in improving the electrochemical reaction kinetics. When used as cathode materials for Li-S batteries, the S@Co 9 S 8 composite cathode exhibits high capacity and an exceptional stable cycling life demonstrated by tests of 600 cycles at 1 C with a very low capacity decay rate of only ≈0.026% per cycle.

Novel KTiO is successfully fabricated via a facile hydrothermal method combined with a subsequent annealing treatment and further evaluated as an anode material for potassium-ion batteries for the first time. This study may provide a broader vision into developing anode materials for potassium-ion batteries.