Search

High‐entropy oxides (HEOs) have been showing great promise in a wide range of applications. There remains a lack of clarity regarding the influence of nanostructure and composition on their Li storage performance. Herein, a dealloying technique to synthesize hierarchical nanoporous HEOs with tunable compositions is employed. Building upon the extensively studied quinary AlFeNiCrMnOx, an additional element (Co, V, Ti, or Cu) is introduced to create senary HEOs, allowing for investigation of the impact of the added component on Li storage performance. With higher specific surface areas and oxygen vacancy concentrations, all their HEOs exhibit high Li storage performances. Remarkably, the senary HEO with the addition of V (AlNiFeCrMnVOx) achieves an impressive capacity of 730.2 mAh g−1 at 2.0 A g−1, which surpasses all reported performance of HEOs. This result demonstrates the synergistic interaction of the six elements in one HEO nanostructure. Additionally, the battery cycling‐induced reconstruction and cation diffusion in the HEOs is uncovered, which results in an initial capacity decrease followed by a subsequent continuous capacity increase and enhanced Li ion diffusion. The results highlight the crucial roles played by both nanoporous structure design and composition optimization in enhancing Li storage of HEOs. [ABSTRACT FROM AUTHOR]

Secondary Zn-ion batteries (ZIBs) using aqueous electrolytes are very promising for safe and large-scale energy storage in the future. However, we still lack suitable cathode materials with high energy density and durability for Zn2+ storage. Herein, a three-dimensional nanoporous microellipsoid Mn2O3 covered with an ultrathin layer of polyaniline (PANI) composite (Mn2O3/PANI) is developed for advanced ZIBs. The synthesis of Mn2O3/PANI is quite easy: nanoporous Mn2O3 (which is obtained from the pyrolysis of MnCO3) is immersed into aniline, and the subsequent self-initiated polymerization of PANI will cover the Mn2O3 surface. The bicontinuous nanoporous structure with a pore size of ∼30 nm facilitates ion diffusion and provides an active interface for fast zinc-ion storage. Moreover, the uniformly coated ultrathin PANI cover not only inhibits Mn2O3 dissolution and protects the structural integrity but also provides a fast electron transport network during charge/discharge. Consequently, the designed Mn2O3/PANI achieves a high energy capacity, a high rate performance, and a much longer lifetime (86.6% capacity retention over 2000 cycles at 1 A g–1), outperforming those of most reported cathode materials. Detailed electrochemical studies and characterizations demonstrate that the H+ and Zn2+ coinsertion mechanism and the PANI cover can enlarge the Zn-ion diffusion coefficient. This work introduces a facile route to develop 3D bicontinuous nanoporous Mn2O3/PANI composites for highly reversible ZIBs. [ABSTRACT FROM AUTHOR]

High‐entropy alloys (HEAs) have attracted widespread attention as both structural and functional materials owing to their huge multielement composition space and unique high‐entropy mixing structure. Recently, emerging HEAs, either in nano or highly porous bulk forms, are developed and utilized for various catalytic and clean energy applications with superior activity and remarkable durability. Being catalysts, HEAs possess some unique advantages, including (1) a multielement composition space for the discovery of new catalysts and fine‐tuning of surface adsorption (i.e., activity and selectivity), (2) diverse active sites derived from the random multielement mixing that are especially suitable for multistep catalysis, and (3) a high‐entropy stabilized structure that improves the structural durability in harsh catalytic environments. Benefited from these inherent advantages, HEA catalysts have demonstrated superior catalytic performances and are promising for complex carbon (C) and nitrogen (N) cycle reactions featuring multistep reaction pathways and many different intermediates. However, the design, synthesis, characterization, and understanding of HEA catalysts for C‐ and N‐involved reactions are extremely challenging because of both complex high‐entropy materials and complex reactions. In this review, we present the recent development of HEA catalysts, particularly on their innovative and extensive syntheses, advanced (in situ) characterizations, and applications in complex C and N looping reactions, aiming to provide a focused view on how to utilize intrinsically complex catalysts for these important and complex reactions. In the end, remaining challenges and future directions are proposed to guide the development and application of HEA catalysts for highly efficient energy storage and chemical conversion toward carbon neutrality. [ABSTRACT FROM AUTHOR]

Developing highly active and durable electrocatalysts for acidic oxygen evolution reaction remains a great challenge due to the sluggish kinetics of the four-electron transfer reaction and severe catalyst dissolution. Here we report an electrochemical lithium intercalation method to improve both the activity and stability of RuO2 for acidic oxygen evolution reaction. The lithium intercalates into the lattice interstices of RuO2, donates electrons and distorts the local structure. Therefore, the Ru valence state is lowered with formation of stable Li-O-Ru local structure, and the Ru–O covalency is weakened, which suppresses the dissolution of Ru, resulting in greatly enhanced durability. Meanwhile, the inherent lattice strain results in the surface structural distortion of LixRuO2 and activates the dangling O atom near the Ru active site as a proton acceptor, which stabilizes the OOH* and dramatically enhances the activity. This work provides an effective strategy to develop highly efficient catalyst towards water splitting. While water splitting in acid offers higher operational performances than in alkaline conditions, there are few high-activity, acid-stable oxygen evolution electrocatalysts. Here, authors examine electrochemical Li intercalation to improve the activity and stability of RuO2 for acidic water oxidation. [ABSTRACT FROM AUTHOR]

Catalyzing oxygen reduction reaction (ORR) and accelerating oxygen diffusion are two key challenges for the requirements of the cathode catalysts in the metal‐air batteries. A promising strategy for improving both ORR performance and mass diffusion simultaneously is to build carbon‐based catalysts with ORR‐active chemical dopants and 3D interconnected porosity. Herein, a 3D nanoporous N‐doped carbon with bicontinuous porosity and interconnected open‐pore channels is reported, which is prepared by a polyaniline‐assisted template method. The polyaniline can efficiently inhibit the surface diffusion‐caused template coarsening, achieving a small pore size of 35 nm. The small porous morphology gives rise to a high N‐dopant concentration up to 7.20 at.%, which in turn exhibits a commercial Pt/C‐comparable ORR performance together with satisfied durability in alkaline media. Using these nanoporous carbon catalysts as air electrodes, an all‐solid‐state flexible Al‐air battery is assembled with the measured maximum power density reaching 130.5 mW cm−2, as compared to 106.2 mW cm−2 when the commercial Pt/C standard is used. This study provides an efficient method to synthesize 3D N‐doped carbon with bicontinuous nano‐sized pore channels for wide‐ranging applications in portable and flexible devices. [ABSTRACT FROM AUTHOR]

Alkaline anion exchange membrane (AEM) water electrolysis is currently the most promising hydrogen production technology, and the development of non‐precious metal‐based hydrogen evolution reaction (HER) electrocatalysts with high performance and low price is one of the greatest challenges for large‐scale AEM. Although the reaction mechanism of HER under alkaline conditions is very different from acidic conditions, many researchers still believe that the HER activity is determined by Gibbs free energy for hydrogen absorption (ΔGH*) in all pH environments. In the meantime, vanadium‐based nitrides are rarely reported as alkaline HER catalysts due to the large density unoccupied orbitals of V cause high ΔGH* value. Herein, we prepare nanoporous VN sheet arrays (NSAs) with high specific surface by hydrothermal‐nitriding treatment, and then optimize its electronic structure via varying the doping amount of Co. As a result, the Co doped VN NSAs display an outstanding HER performance (overpotential of 37 mV at 10 mA cm−2 and Tafel slope of 41 mV dec−1), which is even close to the commercial Pt/C catalyst under alkaline conditions. Moreover, by combining theoretical calculations and HER performances under acid and basic conditions, we find that the adsorption/desorption of hydrogen on activity sites could not fully revealed by ΔGH*. This work opens up a new door to understand the mechanism of alkaline HER reaction and the development of HER electrocatalysts. [ABSTRACT FROM AUTHOR]

As in many other electrochemical energy‐converting systems, the flexible direct ethanol fuel cells rely heavily on high‐performance catalysts with low noble metal contents and high tolerance to poisoning. In this work, a generic dealloying procedure to synthesize nanoporous multicomponent anodic and cathodic catalysts for the high‐performance ethanol fuel cells is reported. On the anode side, the nanoporous AlPdNiCuMo high‐entropy alloy exhibits an electrochemically active surface area of 88.53 m2 g−1Pd and a mass activity of 2.67 A mg−1Pd for the ethanol oxidation reaction. On the cathode side, the dealloyed spinel (AlMnCo)3O4 nanosheets with no noble metals demonstrate a comparable catalytic performance as the standard Pt/C for the oxygen reduction reaction, and tolerance to high concentrations of ethanol. Equipped with such anodic and cathodic catalysts, the flexible solid‐state ethanol fuel cell is able to deliver an ultra‐high energy density of 13.63 mWh cm−2 with only 3 mL ethanol, which is outstanding compared with other similar solid‐state energy devices. Moreover, the solid‐state ethanol fuel cell is highly flexible, durable and exhibits an inject‐and‐run function. [ABSTRACT FROM AUTHOR]

An electrode with low performance or limited endurance for water splitting hydrogen generation has been the key limitation for application of hydrogen in contemporary clean-energy technologies. In this paper, an Al80Ni6Co3Mn3Y5Au3 metallic glass ribbon with outstanding catalytic activity in the hydrogen evolution reaction (HER) in acidic solutions is fabricated for the first time. Its overpotential is about 70 mV @ 10 mA cm−2 and Tafel slope is about 39 mV dec−1, which are comparable to those of commercial noble Pt/C electrodes (33 mV @ 10 mA cm−2 and 38 mV dec−1). Such a high catalytic reactivity is attributed to the synergic effect of multiple elements that disperse atomically homogeneously on the nanoporous surface. The outstanding catalytic activity persists and even becomes much better over a long-time reaction, which is attributed to the formation of a protective Au-rich layer in the interface. The Al-based metallic glass ribbon is flexible with high yield strength, large elasticity and good electrical conductivity, which are desirable and promising characteristics for a free-standing catalytic electrode in the HER. [ABSTRACT FROM AUTHOR]

Controllably incorporating multiple immiscible metal elements into one single nanostructure has immeasurable technological and scientific potential, but it remains a challenge for the conventional bottom-up synthetic methods. Herein, we presented a general and scalable route to prepare multi-component nanostructured alloys referred to as nanoporous high-entropy alloys (np-HEAs) by combining bulk melting, fast cooling, and dealloying. To demonstrate this concept, we synthesized senary AlNiCuPtPdAu, octonary AlNiCuPtPdAuCoFe, and senary all-non-noble metal AlNiCuMoCoFe np-HEA with ligament sizes of ∼2–3 nm and precisely controlled composition by dealloying the designed precursor alloys. With a naturally formed thin oxide layer of spinel γ-Al2O3, AlNiCuPtPdAu np-HEA exhibited greatly enhanced high-temperature stability (up to 600 °C) and CO oxidation activity. Interestingly, with the removal of the surface oxide layer, np-HEA still showed good resistance to coarsening at 200 °C for 10 h due to its intrinsically low diffusivity originating from the multiple-principal-element mixing effect. For electrocatalysis, np-HEA with a low Pt loading amount exhibited 10 times the mass activity of Pt/C for oxygen reduction reaction and maintained 92.5% of its initial activity after 100k electrochemical cycles. [ABSTRACT FROM AUTHOR]