Self-templating synthesis and structural regulation of nanoporous rhodium-nickel alloy nanowires efficiently catalyzing hydrogen evolution reaction in both acidic and alkaline electrolytes

Highly active and stable electrocatalysts to produce hydrogen through water splitting are crucial for clean energy systems but are still challenging.Herein,a novel self-templating strategy was proposed to synthesize one-dimensional nanoporous RhNi alloy nanowires through combining metallurgical eutectic solidification and microalloying with chemical dealloying.In-situ X-ray diffraction and ex-situ characterizations reveal that the Al matrix served as a template to guide the growth of the Al3(Ni,Rh)nanowires during eutectic solidification of Al-Ni-Rh precursor and was completely removed in the dealloying process.Meanwhile,the nanowire morphology could be well retained and the dealloying of Al_(3)(Ni,Rh)led to the formation of nanoporous RhNi alloy nanowires.The length scale of the RhNi nanowires could be facilely regulated by changing the solidification conditions.More importantly,the RhNi catalysts show excellent electrocatalytic activity and stability towards hydrogen evolution reaction in both acidic and alkaline media,which has been rationalized by density functional theory calculations.

Amorphous germanium-crystalline bismuth films as a promising anode for magnesium-ion batteries

Magnesium-ion batteries(MIBs)are promising alternatives to lithium-ion batteries due to their safety and high theoretical specific capacity,and the abundance of magnesium reserves.However,their anodes and electro-lytes severely restrict the development of MIBs,so alloy-type anodes provide an effective strategy to circum-vent the surface passivation issue encountered with Mg metal in conventional electrolytes.Theoretically,a germanium anode can deliver a high specific capacity of 1476 mAh g?1,but hitherto,no experimental reports have described Ge in MIBs.Herein,we experimentally verified that Ge could reversibly react with Mg 2þions through the design of dual-phase Ge–Bi film electrodes fabricated by magnetron co-sputtering.Notably,a Ge 57 Bi 43 electrode delivered a high specific capacity of 847.5 mAh g?1,owing to the joint alloying reactions of Ge and Bi with Mg,which was much higher than the specific capacity of Bi(around 385 mAh g?1).Moreover,the Ge–Bi anode showed excellent rate performance,good cycling stability,and superior compatibility with conventional electrolytes such as Mg(TFSI)2.More importantly,the Mg storage mechanism of the Ge–Bi anode was unveiled by operando X-ray diffraction,and density functional theory calculations rationalized that the introduction of Bi to form Ge–Bi evidently decreased the defect formation energy and effectively boosted the electrochemical reactivity of Ge with Mg.

Phase-boundary regulation boosting electrochemical reactivity of tin-based anodes for magnesium-ion batteries

Tin(Sn)-based materials are promising anodes for magnesium-ion batteries(MIBs) owing to their low reaction voltages, high theoretical specific capacities and good compatibility with conventional electrolytes. However, relatively arduous alloying reaction and sluggish diffusion kinetics limit their practical applications. Herein, we proposed a general strategy to regulate the electrochemical reactivity and performance of Sn-based anodes for Mg storage through the introduction of the second phase and phase boundary. The biphase Sn–Al, Sn–Pb and Sn–Zn O films were further fabricated via magnetron co-sputtering. Taking Sn–Al as an example, it has been revealed that the introduction of Al can effectively stimulate the electrochemical reaction of Sn with Mg in either nanoscale or bulk through combining experiments with density-functional theory calculations. Specially, the rolled Sn–Al electrode exhibits superior long-term stability over 5,000 cycles. Additionally, the Mg-storage mechanism of the Sn–Al electrode was investigated by operando X-ray diffraction. The Sn–Al anodes also demonstrate good compatibility with simple Mg-salt-based electrolytes like Mg(TFSI)2in full cells. More importantly, it has been authenticated that the activation effect of second phase and phase boundary to Sn is also applicable to Pb and Zn O. Our findings may provide a favorable reference for the development of alloy-type anodes for MIBs.

Self-supporting nanoporous gold-palladium overlayer bifunctional catalysts toward oxygen reduction and evolution reactions

The oxygen reduction reaction （ORR） and oxygen evolution reaction （OER） are crucial processes for energy conversion/storage systems, such as fuel cells, metal-air batteries, and water splitting. However, both reactions are severely restricted by their sluggish kinetics, thus requiring highly active, cost-effective, and durable electrocatalysts. Herein, we develop novel bifunctional nanocatalysts through surface nanoengineering of dealloying-driven nanoporous gold （NPG）. Pd overlayers were precisely deposited onto the NPG ligament surface by epitaxial layer-by-layer growth. More importantly, the obtained NPG-Pd overlayer nanocatalysts exhibit remarkably enhanced electrocatalytic activities toward both the ORR and OER in alkaline media, benchmarked against a state- of-the-art Pt/C catalyst. The improved electrocatalytic performance is rationalized by the unique three-dimensional nanoarchitecture of NPG, enhanced Pd utilization efficiency from precise control of the Pd overlayers, and change in electronic structure, as revealed by density functional theory calculations.

Tungsten diselenide nanoplates as advanced lithium/ sodium ion electrode materials with different storage mechanisms

Transition-metal dichalcogenides （TMDs） exhibit immense potential as lithium/ sodium-ion electrode materials owing to their sandwich-like layered structures. To optimize their lithium/sodium-storage performance, two issues should be addressed： fundamentally understanding the chemical reaction occurring in TMD electrodes and developing novel TMDs. In this study, WSe2 hexagonal nanoplates were synthesized as lithium/sodium-ion battery （LIB/SIB） electrode materials. For LIBs, the WSe2-nanoplate electrodes achieved a stable reversible capacity and a high rate capability, as well as an ultralong cycle life of up to 1,500 cycles at 1,000 mA·g^-1. Most importantly, in situ Raman spectroscopy, ex situ X-ray diffraction （XRD）, transmission electron microscopy, and electrochemical impedance spectroscopy measurements performed during the discharge-charge process clearly verified the reversible conversion mechanism, which can be summarized as follows： WSe2 ＋ 4Li^＋ ＋ 4e^- ←→ W ＋ 2Li2Se. The WSe2 nanoplates also exhibited excellent cycling performance and a high rate capability as SIB electrodes. Ex situ XRD and Raman spectroscopy results demonstrate that WSe2 reacted with Na^＋ more easily and thoroughly than with Li^＋ and converted to Na2Se and tungsten in the Ist sodiated state. The subsequent charging reaction can be expressed as Na2Se → Se ＋ 2Na^＋＋ 2e^-, which differs from the traditional conversion mechanism for LIBs. To our knowledge, this is the first systematic exploration of the lithium/sodium-storage performance of WSe2 and the mechanism involved.

Multicomponent platinum-free nanoporous Pd-based alloy as an active and methanol-tolerant electrocatalyst for the oxygen reduction reaction

Development of high-performance oxygen reduction reaction （ORR） catalysts is crucial to improve proton exchange membrane fuel cells. Herein, a multicomponent nanoporous PdCuTiA1 （np-PdCuTiA1） electrocatalyst has been synthesized by a facile one-step dealloying strategy. The np-PdCuTiA1 catalyst exhibits a three-dimensional bicontinuous interpenetrating ligament/channel structure with an ultrafine length scale of -3.7 nm. The half-wave potential of np PdCuTiA1 is 0.873 V vs. RHE, more positive than those of PdC （0.756 V vs. RHE） and PtC （0.864 V vs. RHE） catalysts. The np-PdCuTiAl alloy shows a 4-electron reaction pathway with similar Tafel slopes to PtC. Remarkably, the half-wave potential shows a negative shift of only 12 mV for np-PdCuTiA1 in the presence of methanol, and this negative shift is much lower than those of the PdC （50 mV） and PtC （165 mV） catalysts. The enhanced ORR activity of np-PdCuTiA1 has been further rationalized through density functional theory calculations.