Monolithic Nickel Catalyst Featured with High-Density Crystalline Steps for Stable Hydrogen Evolution at Large Current Density.

Producing hydrogen via electrochemical water splitting with minimum environmental harm can help resolve the energy crisis in a sustainable way. Here, this work fabricates the pure nickel nanopyramid arrays (NNAs) with dense high-index crystalline steps as the cata electrode via a screw dislocation-dominated growth kinetic for long-term durable and large current density hydrogen evolution reaction. Such a monolithic NNAs electrode offers an ultralow overpotential of 469 mV at a current density of 5000 mA cm-2 in 1.0 m KOH electrolyte and shows a high stability up to 7000 h at a current density of 1000 mA cm-2 , which outperforms the reported catas and even the commercial platinum cata for long-term services under high current densities. Its unique structure can substantially stabilize the high-density surface crystalline steps on the catalytic electrode, which significantly elevates the catalytic activity and durability of nickel in an alkaline medium. In a typical commercial hydrogen gas generator, the total energy conversion rate of NNAs reaches 84.5% of that of a commercial Pt/Ti cata during a 60-day test of hydrogen production. This work approach can provide insights into the development of industry-compatible long-term durable, and high-performance non-noble metal catas for various applications.

Ensemble Effect of Ruthenium Single-Atom and Nanoparticle Catalysts for Efficient Hydrogen Evolution in Neutral Media.

Hydrogen evolution reaction (HER) plays a key role in electrochemical water splitting, which is a sustainable way for hydrogen production. The kinetics of HER is sluggish in neutral media that requires noble metal catalysts to alleviate energy consumption during the HER process. Here, we present a catalyst comprising a ruthenium single atom (Ru1) and nanoparticle (Run) loaded on the nitrogen-doped carbon substrate (Ru1-Run/CN), which exhibits excellent activity and superior durability for neutral HER. Benefiting from the synergistic effect between single atoms and nanoparticles in the Ru1-Run/CN, the catalyst exhibits a very low overpotential down to 32 mV at a current density of 10 mA cm-2 while maintaining excellent stability up to 700 h at a current density of 20 mA cm-2 during the long-term test. Computational calculations reveal that, in the Ru1-Run/CN catalyst, the existence of Ru nanoparticles affects the interactions between Ru single-atom sites and reactants and thus improves the catalytic activity of HER. This work highlights the ensemble effect of electrocatalysts for HER and could shed light on the rational design of efficient catalysts for other multistep electrochemical reactions.

Coordination modulation of iridium single-atom catalyst maximizing water oxidation activity.

Single-atom catalysts (SACs) have attracted tremendous research interests in various energy-related fields because of their high activity, selectivity and 100% atom utilization. However, it is still a challenge to enhance the intrinsic and specific activity of SACs. Herein, we present an approach to fabricate a high surface distribution density of iridium (Ir) SAC on nickel-iron sulfide nanosheet arrays substrate (Ir1/NFS), which delivers a high water oxidation activity. The Ir1/NFS catalyst offers a low overpotential of ~170 mV at a current density of 10 mA cm-2 and a high turnover frequency of 9.85 s-1 at an overpotential of 300 mV in 1.0 M KOH solution. At the same time, the Ir1/NFS catalyst exhibits a high stability performance, reaching a lifespan up to 350 hours at a current density of 100 mA cm-2. First-principles calculations reveal that the electronic structures of Ir atoms are significantly regulated by the sulfide substrate, endowing an energetically favorable reaction pathway. This work represents a promising strategy to fabricate high surface distribution density single-atom catalysts with high activity and durability for electrochemical water splitting.

Electrolyte Solvation Manipulation Enables Unprecedented Room-Temperature Calcium-Metal Batteries.

Calcium-metal batteries (CMBs) provide a promising option for high-energy and cost-effective energy-storage technology beyond the current state-of-the-art lithium-ion batteries. Nevertheless, the development of room-temperature CMBs is significantly impeded by the poor reversibility and short lifespan of the calcium-metal anode. A solvation manipulation strategy is reported to improve the plating/stripping reversibility of calcium-metal anodes by enhancing the desolvation kinetics of calcium ions in the electrolyte. The introduction of lithium salt changes the electrolyte structure considerably by reducing coordination number of calcium ions in the first solvation shell. As a result, an unprecedented Coulombic efficiency of up to 99.1 % is achieved for galvanostatic plating/stripping of the calcium-metal anode, accompanied by a very stable long-term cycling performance over 200 cycles at room temperature. This work may open up new opportunities for development of practical CMBs.

Enabling High-Voltage Lithium Metal Batteries by Manipulating Solvation Structure in Ester Electrolyte.

Lithium metal is an ideal electrode material for future rechargeable lithium metal batteries. However, the widespread deployment of metallic lithium anode is significantly hindered by its dendritic growth and low Coulombic efficiency, especially in ester solvents. Herein, by rationally manipulating the electrolyte solvation structure with a high donor number solvent, enhancement of the solubility of lithium nitrate in an ester-based electrolyte is successfully demonstrated, which enables high-voltage lithium metal batteries. Remarkably, the electrolyte with a high concentration of LiNO3 additive presents an excellent Coulombic efficiency up to 98.8 % during stable galvanostatic lithium plating/stripping cycles. A full-cell lithium metal battery with a lithium nickel manganese cobalt oxide cathode exhibits a stable cycling performance showing limited capacity decay. This approach provides an effective electrolyte manipulation strategy to develop high-voltage lithium metal batteries.

A Hollow-Structured Manganese Oxide Cathode for Stable Zn-MnO2 Batteries.

Aqueous rechargeable zinc-manganese dioxide (Zn-MnO2) batteries are considered as one of the most promising energy storage devices for large scale-energy storage systems due to their low cost, high safety, and environmental friendliness. However, only a few cathode materials have been demonstrated to achieve stable cycling for aqueous rechargeable Zn-MnO2 batteries. Here, we report a new material consisting of hollow MnO2 nanospheres, which can be used for aqueous Zn-MnO2 batteries. The hollow MnO2 nanospheres can achieve high specific capacity up to ~405 mAh g−1 at 0.5 C. More importantly, the hollow structure of birnessite-type MnO2 enables long-term cycling stability for the aqueous Zn-MnO2 batteries. The excellent performance of the hollow MnO2 nanospheres should be due to their unique structural properties that enable the easy intercalation of zinc ions.

Fabrication of Nanoporous Nickel-Iron Hydroxylphosphate Composite as Bifunctional and Reversible Catalyst for Highly Efficient Intermittent Water Splitting.

Global-scale application of water-splitting technology for hydrogen fuel production and storage of intermittent renewable energy sources has called for the development of oxygen- and hydrogen-evolution catalysts that are inexpensive, efficient, robust, and can withstand frequent power interruptions and shutdowns. Here, we report the controlled electrodeposition of porous nickel-iron hydroxylphosphate (NiFe-OH-PO4) nanobelts onto the surface of macroporous nickel foams (NF) as a bifunctional electrocatalyst for efficient whole-cell water electrolysis. The NiFe-OH-PO4/NF electrode shows both high water oxidation and water reduction catalytic activity in alkaline solutions and is able to deliver current densities of 20 and 800 mA cm-2 at overpotentials of merely 249 and 326 mV for oxygen-evolution reaction, current densities of 20 and 300 mA cm-2 at overpotentials of only 135 and 208 mV for hydrogen-evolution reaction. Further, in a two-electrode water electrolytic cell, the bifunctional NiFe-OH-PO4/NF electrodes can obtain the current densities of 20 and 100 mA cm-2 at an overall cell potential of only 1.68 and 1.91 V, respectively. Remarkably, the NiFe-OH-PO4/NF catalyst also represents prolonged stability under both continuous and intermittent electrolysis and can be used for oxygen evolution and hydrogen evolution reversibly without degradation.