Germanium is a promising high-capacity anode material for lithium ion batteries, but it usually exhibits poor cycling stability because of its huge volume variation during the lithium uptake and release process. A double protection strategy to improve the electrode performance of Ge through the use of Ge@C core-shell nanostructures and reduced graphene oxide (RGO) networks has been developed. The as-synthesized Ge@C/RGO nanocomposite showed excellent cycling performance and rate capability in comparison with Ge@C nanoparticles when used as an anode material for Li ion batteries, which can be attributed to the electronically conductive and elastic RGO networks in addition to the carbon shells and small particle sizes of Ge. The strategy is simple yet very effective, and because of its versatility, it may be extended to other high-capacity electrode materials with large volume variations and low electrical conductivities.

The design of low-cost yet high-efficiency electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) over a wide pH range is highly challenging. We now report a hierarchical co-assembly of interacting MoS 2 and Co 9 S 8 nanosheets attached on Ni 3 S 2 nanorod arrays which are supported on nickel foam (NF). This tiered structure endows high performance toward HER and OER over a very broad pH range. By adjusting the molar ratio of the Co:Mo precursors, we have created CoMoNiS-NF-xy composites (x:y means Co:Mo molar ratios ranging from 5:1 to 1:3) with controllable morphology and composition. The three-dimensional composites have an abundance of active sites capable of universal pH catalytic HER and OER activity. The CoMoNiS-NF-31 demonstrates the best electrocatalytic activity, giving ultralow overpotentials (113, 103, and 117 mV for HER and 166, 228, and 405 mV for OER) to achieve a current density of 10 mA cm −2 in alkaline, acidic, and neutral electrolytes, respectively. It also shows a remarkable balance between electrocatalytic activity and stability. Based on the distinguished catalytic performance of CoMoNiS-NF-31 toward HER and OER, we demonstrate a two-electrode electrolyzer performing water electrolysis over a wide pH range, with low cell voltages of 1.54, 1.45, and 1.80 V at 10 mA cm −2 in alkaline, acidic, and neutral media, respectively. First-principles calculations suggest that the high OER activity arises from electron transfer from Co 9 S 8 to MoS 2 at the interface, which alters the binding energies of adsorbed species and decreases overpotentials. Our results demonstrate that hierarchical metal sulfides can serve as highly efficient all-pH (pH = 0−14) electrocatalysts for overall water splitting.

Rechargeable batteries are important energy storage devices for the integration of renewable resources. [1][2][3][4][5][6][7][8][9][10] Lithium-ion batteries (LIBs) represent the state-of-the-art technology in high-energy batteries and have been widely applied in portable electronic devices. [11][12][13][14][15][16][17][18][19] However, the limited mineral reserves and high cost of lithium-based compounds hinder their expanded application in large-scale energy storage. To address this issue, rechargeable sodium-ion batteries (SIBs) working at room temperature are proposed as potential alternatives for large-scale energy storage, in particular for smart electric grids, because of the abundant supply and low cost of sodium. [20][21][22][23] Although the storage mechanism of Na in electrode materials is expected to be similar to that of Li, most commonly used electrode materials for LIBs are diffi cult to insert Na + because of the large radius of Na + (55% larger than that of Li + ). [24][25][26][27] To date, most research has focused on developing cathode materials with large interstitial space in the crystallographic structures, [28][29][30] while much less has been devoted to the anode materials.Sodium alloys, titanates, and carbonaceous materials have been investigated as anode materials. Sodium alloys are hindered by the large volume expansion of Sn (520%) [ 31 ] and Sb (390%) [ 32 ] during the sodiation, while titanates usually deliver relatively low capacity. [ 33 ] Therefore, carbonaceous materials are regarded as the most promising candidates for SIBs. However, graphite, the dominant commercial anode material in LIBs, is unsuitable for the intercalation of Na + because of its small interlayer distance. On the contrary, carbon materials with low graphitization turn out to be more suitable for Na + storage because of their large interlayer distance and disordered structure. [34][35][36][37][38] Cao and co-workers calculated that the critical interlayer distance for the Na + insertion should be over 0.37 nm for the carbonaceous materials. [ 39 ] Dahn and co-workers demonstrated that a reversible capatcity of 300 mA h g −1 can be obtained for hard-carbon material and proposed that Na + can insert into the random stacking layers of hard carbon and the nanoporosity between randomly stacked layers. [ 40 ] Although some achievement has been obtained for hard carbon as anode materials for SIBs, their capacity and high-rate capability still require improvement because of their intrinsically low graphitization. Additionally, their cycle stabilities are insuffi cient for the practical application in SIBs. It should also be noted that most of the capacity for hard carbon derives from the low-potential region (around 0 V), close to the Na plating potential, which may cause safety issues during fast charging process.Designing hierarchically porous structures effectively improves the electrochemical performance of carbonaceous materials in LIBs because of their decreased diffusion distance for Li + . [ 41,42 ] The chemica...