The catalytic coordinate is essentially the evolving frontier orbital interaction while feeding with catalytic materials and adsorbates under proper reaction conditions. The heterogeneous catalytic reaction mechanism involves the initial adsorption and activation of reactants, subsequent intermediate transformation, final target product desorption, and regeneration of catalytic materials. In these catalytic processes, interaction modulations in terms of orbital hybridization/coupling allow an intrinsic control on both thermodynamics and kinetics. Concerned charge transfer and redistribution, orbital splitting and rearrangement with specific orientation, and spin change and crossover pose a formidable challenge on mechanism elucidation; it is hard to precisely correlate the apparent activity and selectivity, let alone rational modulations on it. Therefore, deciphering the orbital couplings inside a catalytic round is highly desirable and the dependent descriptor further provides in‐depth insights into catalyst design at the molecule orbital level. This review hopes to provide a comprehensive understanding on orbital hybridizations, modulations, and correlated descriptors in heterogeneous catalysis.
Electrochemical water splitting for hydrogen generation is considered one of the most promising strategies for reducing the use of fossil fuels and storing renewable electricity in hydrogen fuel. However, the anodic oxygen evolution process remains a bottleneck due to the remarkably high overpotential of about 300 mV to achieve a current density of 10 mA cm-2. The key to solving this dilemma is the development of highly efficient catalysts with minimized overpotential, long-term stability, and low cost. As a new 2D material, MXene has emerged as an intriguing material for future energy conversion technology due to its benefits, including superior conductivity, excellent hydrophilic properties, high surface area, versatile chemical composition, and ease of processing, which make it a potential constituent of the oxygen evolution catalyst layer. This review aims to summarize and discuss the recent development of oxygen evolution catalysts using MXene as a component, emphasizing the synthesis and synergistic effect of MXene-based composite catalysts. Based on the discussions summarized in this review, we also provide future research directions regarding electronic interaction, stability, and structural evolution of MXene-based oxygen evolution catalysts. We believe that a broader and deeper research in this area could accelerate the discovery of efficient catalysts for electrochemical oxygen evolution.
With exceptional capacity during high-voltage cycling, P3-type Nadeficient layered oxide cathodes have captured substantial attention. Nevertheless, they are plagued by severe capacity degradation over cycling. In this study, tuning and optimizing the phase composition in layered oxides through Li incorporation are proposed to enhance the high-voltage stability. The structural dependence of layered Na2/3LixNi0.25Mn0.75O2+δ oxides on the lithium content (0.0 ≤ x ≤ 1.0) offered during synthesis is investigated systematically on an atomic scale. Surprisingly, increasing the Li content triggers the formation of mixed P2/O3-type or P3/P2/O3-type layered phases. As the voltage window is 1.5–4.5 V, P3-type Na2/3Ni0.25Mn0.75O2 (NL0.0NMO,
Efficient redox reactions of lean electrolyte lithium–sulfur (Li–S) batteries highly rely on rational catalyst design. Herein, we report an electrocatalyst based on N-doped carbon nanotubes (CNT)-encapsulated Ni nanoparticles (Ni@NCNT) as kinetics regulators for Li–S batteries to propel the polysulfide-involving multiphase transformation. Moreover, such a CNT-encapsulation strategy greatly prevents the aggregation of Ni nanoparticles and enables the extraordinary structural stability of the hybrid electrocatalyst, which guarantees its persistent catalytic activity on sulfur redox reactions. When used as a modified layer on a commercial separator, the Ni@NCNT interlayer contributes to stabilizing S cathode and Li anode by significantly retarding the shuttle effect. The corresponding batteries with a 3.5 mg cm-2 sulfur loading achieve the promising cycle stability with ∼85% capacity retention at the electrolyte/sulfur ratios of 5 and 3 µL mg-1. Even at a high loading of 12.2 mg cm-2, the battery affords an areal capacity of 7.5 mA h cm-2.
Electrochemical hydrogen evolution reaction (HER) and overall water splitting (OWS) for renewable energy generation have recently become a highly promising and sustainable strategy to tackle energy crisis and global warming arising from our overreliance on fossil fuels. Previously, tremendous research breakthroughs have been made in 2D carbon-based heterostructured electrocatalysts in this field. Such heterostructures are distinguished by their remarkable electrical conductivity, exposed active sites, and mechanical stability. Herein, with fundamental mechanisms of electrocatalytic OWS summarized, our review critically emphasized on state-of-the-art 2D carbon nanosheet-, graphene-, and graphdiyne-based heterostructured electrocatalysts in HER and OWS since 2018. Particularly, the three emerging carbonaceous substrates tend to be incorporated with metal carbides, phosphides, dichalcogenides, nitrides, oxides, nanoparticles, single atom catalysts, or layered double hydroxides. Meanwhile, fascinating structural engineering and facile synthesis strategies were also unraveled to establish the structure–activity relationship, which will enlighten future electrocatalyst developments toward ameliorated HER and OWS activities. Additionally, computational results from density functional theory simulations were highlighted as well to better comprehend the synergistic effects within the heterostructures. Finally, current stages and future recommendations of this brand-new electrocatalyst type were concluded and discussed for advanced catalyst designs and future practical applications.
The industrial application of zinc-ion batteries is restricted by irrepressibledendrite growth and side reactions that resulted from the surfaceheterogeneity of the commercial zinc electrode and thethermodynamic spontaneous corrosion in a weakly acidic aqueouselectrolyte. Herein, a common polar dye, Procion Red MX-5b, with highpolarity and asymmetric charge distribution is introduced into the zincsulfate electrolyte, which can not only reconstruct the solvation configurationof Zn+2 and strengthen hydrogen bonding to reduce the reactivityof free H2O but also homogenize interfacial electric field by itspreferentially absorption on the zinc surface. The symmetric cell cancycle with a lower voltage hysteresis (78.4 mV) for 1120 times at5 mA cm−2 and Zn//NaV3O8·1.5H2O full cell can be cycled over 1000 times with high capacity (average 170 mAh g−1) at 4 A g−1 in the compoundelectrolyte. This study provides a new perspective for additiveengineering strategies of aqueous zinc-ion batteries.
Metal–air batteries, fuel cells, and electrochemical H2O2 production currently attract substantial consideration in the energy sector owing to their efficiency and eco-consciousness. However, their broader use is hindered by the complex oxygen reduction reaction (ORR) that occurs at cathodes and involves intricate electron transfers. Despite the significant ORR performance of platinum-based catalysts, their high cost, operational limitations, and susceptibility to methanol poisoning hinder broader implementation. This emphasizes the need for efficient nonprecious metal-based ORR electrocatalysts. A promising approach involves utilizing single-atom catalysts (SACs) featuring metal–nitrogen– carbon (M-N-C) coordination sites. SACs offer advantages such as optimal utilization of metal atoms, uniform active centers, precisely defined catalytic sites, and robust metal–support interactions. However, the symmetrical electron distribution around the central metal atom of a single-atom site (M-N4) often results in suboptimal ORR performance. This challenge can be addressed by carefully tailoring the surrounding environment of the active center. This review specifically focuses on recent advancements in the Fe-N4 environment within Fe-N-C SACs. It highlights the promising strategy of coupling Fe-N4 sites with metal clusters and/or nanoparticles, which enhances intrinsic activity. By capitalizing on the interplay between Fe-N4 sites and associated species, overall ORR performance improved. The review combines findings from experimental studies and density functional theory simulations, covering synthesis strategies for Fe-N-C coupled synergistic catalysts, characterization techniques, and the influence of associated particles on ORR activity. By offering a comprehensive outlook, the review aims to encourage research into high-efficiency Fe single-atom sites coupled synergistic catalysts for real-world applications in the coming years.
Ineffective control of dendrite growth and side reactions on Zn anodessignificantly retards commercialization of aqueous Zn-ion batteries. Unlikeconventional interfacial modification strategies that are primarilyfocused on component optimization or microstructural tuning, herein, wepropose a crystallinity engineering strategy by developing highly crystallinecarbon nitride protective layers for Zn anodes through molten salttreatment. Interestingly, the highly ordered structure along with sufficientfunctional polar groups and pre-intercalated K+ endows the coating withhigh ionic conductivity, strong hydrophilicity, and accelerated ion diffusionkinetics. Theoretical calculations also confirm its enhanced Znadsorption capability compared to commonly reported carbon nitridewith amorphous or semi-crystalline structure and bare Zn. Benefitingfrom the aforementioned features, the as-synthesized protective layerenables a calendar lifespan of symmetric cells for 1100 h and outstandingstability of full cells with capacity retention of 91.5% after 1500 cycles. Thiswork proposes a new conceptual strategy for Zn anode protection.