A universal approach to dual-metal-atom catalytic sites confined in carbon dots for various target reactions.

Here, a molecular-design and carbon dot-confinement coupling strategy through the pyrolysis of bimetallic complex of diethylenetriamine pentaacetic acid under low-temperature is proposed as a universal approach to dual-metal-atom sites in carbon dots (DMASs-CDs). CDs as the "carbon islands" could block the migration of DMASs across "islands" to achieve dynamic stability. More than twenty DMASs-CDs with specific compositions of DMASs (pairwise combinations among Fe, Co, Ni, Mn, Zn, Cu, and Mo) have been synthesized successfully. Thereafter, high intrinsic activity is observed for the probe reaction of urea oxidation on NiMn-CDs. In situ and ex situ spectroscopic characterization and first-principle calculations unveil that the synergistic effect in NiMn-DMASs could stretch the urea molecule and weaken the N-H bond, endowing NiMn-CDs with a low energy barrier for urea dehydrogenation. Moreover, DMASs-CDs for various target electrochemical reactions, including but not limited to urea oxidation, are realized by optimizing the specific DMAS combination in CDs.

Double-atom dealloying-derived Frank partial dislocations in cobalt nanocatalysts boost metal-air batteries and fuel cells.

Oxygen reduction reaction (ORR), an essential reaction in metal-air batteries and fuel cells, still faces many challenges, such as exploiting cost-effective nonprecious metal electrocatalysts and identifying their surface catalytic sites. Here we introduce bulk defects, Frank partial dislocations (FPDs), into metallic cobalt to construct a highly active and stable catalyst and demonstrate an atomic-level insight into its surface terminal catalysis. Through thermally dealloying bimetallic carbide (Co3ZnC), FPDs were in situ generated in the final dealloyed metallic cobalt. Both theoretical calculations and atomic characterizations uncovered that FPD-driven surface terminations create a distinctive type of surface catalytic site that combines concave geometry and compressive strain, and this two-in-one site intensively weakens oxygen binding. When being evaluated for the ORR, the catalyst exhibits onset and half-wave potentials of 1.02 and 0.90 V (versus the reversible hydrogen electrode), respectively, and negligible activity decay after 30,000 cycles. Furthermore, zinc-air batteries and H2-O2/air fuel cells built with this catalyst also achieve remarkable performance, making it a promising alternative to state-of-the-art Pt-based catalysts. Our findings pave the way for the use of bulk defects to upgrade the catalytic properties of nonprecious electrocatalysts.

PtPd Atomic Layer Shelled PdCu Hollow Nanoparticles on Partially Unzipped Carbon Nanotubes for Breaking the Activity-Stability Trade-Off toward the Hydrogen Oxidation Reaction in Alkaline Media.

Developing highly active yet stable catalysts for the hydrogen oxidation reaction (HOR) in alkaline media remains a significant challenge. Herein, we designed a novel catalyst of atomic PtPd-layer shelled ultrasmall PdCu hollow nanoparticles (HPdCu NPs) on partially unzipped carbon nanotubes (PtPd@HPdCu/W-CNTs), which can achieve a high mass activity, 5 times that of the benchmark Pt/C, and show exceptional stability with negligible decay after 20,000 cycles of accelerated degradation test. The atomically thin PtPd shell serves as the primary active site for the HOR and a protective layer that prevents Cu leaching. Additionally, the HPdCu substrate not only tunes the adsorption properties of the PtPd layer but also prevents corrosive Pt from reaching the interface between NPs and the carbon support, thereby mitigating carbon corrosion. This work introduces a new strategy that leverages the distinct advantages of multiple components to address the challenges associated with slow kinetics and poor durability toward the HOR.

Advanced Nanocarbons Toward two-Electron Oxygen Electrode Reactions for H2O2 Production and Integrated Energy Conversion.

Hydrogen peroxide (H2O2) plays a pivotal role in advancing sustainable technologies due to its eco-friendly oxidizing capability. The electrochemical two-electron (2e-) oxygen reduction reaction and water oxidation reaction present an environmentally green method for H2O2 production. Over the past three years, significant progress is made in the field of carbon-based metal-free electrochemical catalysts (C-MFECs) for low-cost and efficient production of H2O2 (H2O2EP). This article offers a focused and comprehensive review of designing C-MFECs for H2O2EP, exploring the construction of dual-doping configurations, heteroatom-defect coupling sites, and strategic dopant positioning to enhance H2O2EP efficiency; innovative structural tuning that improves interfacial reactant concentration and promote the timely release of H2O2; modulation of electrolyte and electrode interfaces to support the 2e- pathways; and the application of C-MFECs in reactors and integrated energy systems. Finally, the current challenges and future directions in this burgeoning field are discussed.

Under-Coordinated CoFe Layered Double Hydroxide Nanocages Derived from Nanoconfined Hydrolysis of Bimetal Organic Compounds for Efficient Electrocatalytic Water Oxidation.

Hierarchically structured bimetal hydroxides are promising for electrocatalytic oxygen evolution reaction (OER), yet synthetically challenging. Here, the nanoconfined hydrolysis of a hitherto unknown CoFe-bimetal-organic compound (b-MOC) is reported for the controllable synthesis of highly OER active nanostructures of CoFe layered double hydroxide (LDH). The nanoporous structures trigger the nanoconfined hydrolysis in the sacrificial b-MOC template, producing CoFe LDH core-shell octahedrons, nanoporous octahedrons, and hollow nanocages with abundant under-coordinated metal sites. The hollow nanocages of CoFe LDH demonstrate a remarkable turnover frequency (TOF) of 0.0505 s-1 for OER catalysis at an overpotential of 300 mV. It is durable in up to 50 h of electrolysis at step current densities of 10-100 mA cm-2 . Ex situ and in situ X-ray absorption spectroscopic analysis combined with theoretical calculations suggests that under-coordinated Co cations can bind with deprotonated Fe-OH motifs to form OER active Fe-O-Co dimmers in the electrochemical oxidation process, thereby contributing to the good catalytic activity. This work presents an efficient strategy for the synthesis of highly under-coordinated bimetal hydroxide nanostructures. The mechanistic understanding underscores the power of maximizing the amount of bimetal-dimer sites for efficient OER catalysis.

The Underlying Molecular Mechanism of Fence Engineering to Break the Activity-Stability Trade-Off in Catalysts for the Hydrogen Evolution Reaction.

Non-precious-metal (NPM) catalysts often face the formidable challenge of a trade-off between long-term stability and high activity, which has not yet been widely addressed. Herein we propose a distinct molecule-selective fence as a promising concept to solve this activity-stability trade-off. The fence encloses the catalyst and prevents species poisonous to the catalyst from reaching it, but allows catalytic reaction-related species to diffuse freely. We constructed a CoS2 fence layer on the external surface of highly active cobalt-doped MoS2 , achieving a remarkable catalytic stability towards the alkaline hydrogen evolution reaction and improved activity. In situ spectroscopy uncovered the underlying molecular mechanism of the CoS2 fence for breaking the activity-stability trade-off of the MoS2 catalyst. This work offers valuable guidance for rationally designing efficient and stable NPM catalysts.

In Situ Coupling of MnO and Co@N-Doped Graphite Carbon Derived from Prussian Blue Analogous Achieves High-Performance Reversible Oxygen Electrocatalysis for Zn-Air Batteries.

Coupling dual active components into one integrated catalyst as well as understanding their electronic interaction behavior on reversible oxygen electrocatalysis is central to achieving high energy-conversion efficiency for Zn-air batteries (ZABs). Herein, we demonstrate an effective couple of MnO and Co nanocrystals embedded in N-doped graphite carbon to integrate a highly efficient bifunctional catalyst (denoted as MnO/Co@NGC) toward oxygen reduction and evolution reaction (ORR/OER). MnO/Co@NGC was first successfully prepared by the one-step pyrolysis of Mn3[Co(CN)6]2·9H2O@PVP (poly(vinyl pyrrolidone)), and X-ray absorption near-edge structure analysis revealed that the charges were transferred from MnO to Co@NGC, which makes MnO more electrophilic to facilitate the initial electrochemical adsorption of OH- for improving the OER activity. As expected, the as-designed MnO/Co@NGC displays excellent bifunctional ORR/OER activity with a small overpotential gap of only 0.736 V, providing the ZABs with a high trip efficiency of 57.2% as well as excellent cycling stability. This work not only offers a bifunctional ORR/OER electrocatalyst but also further highlights the interfacial charge distribution in oxygen electrocatalysis, affording a promising approach for developing advanced energy-related materials.

Unraveling the Beneficial Microstructure Evolution in Pyrite for Boosted Lithium Storage Performance.

Pyrite FeS2 as a high-capacity electrode material for lithium-ion batteries (LIBs) is hindered by its unstable cycling performance owing to the large volume change and irreversible phase segregation from coarsening of Fe. Here, the beneficial microstructure evolution in MoS2 -modified FeS2 is unraveled during the cycling process; the microstructure evolution is responsible for its significantly boosted lithium storage performance, making it suitable for use as an anode for LIBs. Specifically, the FeS2 /MoS2 displays a long cycle life with a capacity retention of 116 % after 600 cycles at 0.5 A g-1 , which is the best among the reported FeS2 -based materials so far. A series of electrochemical tests and structural characterizations substantially revealed that the introduced MoS2 in FeS2 experiences an irreversible electrochemical reaction and thus the in situ formed metallic Mo could act as the conductive buffer layer to accelerate the dynamics of Li+ diffusion and electron transport. More importantly, it can guarantee the highly reversible conversion in lithiated FeS2 by preventing Fe coarsening. This work provides a fundamental understanding and an effective strategy towards the microstructure evolution for boosting lithium storage performances for other metal sulfide-based materials.

Identifying the Transfer Kinetics of Adsorbed Hydroxyl as a Descriptor of Alkaline Hydrogen Evolution Reaction.

The key descriptor that dominates the kinetics of the alkaline hydrogen evolution reaction (HER) has not yet been unequivocally identified. Herein, we focus on the adsorbed hydroxyl (OHad ) transfer process (OHad + e- ⇄ OH- ) and reveal its crucial role in promoting the overall kinetics of alkaline HER based on Ni/Co-modified MoSe2 model catalysts (Ni-MoSe2 and Co-MoSe2 ) that feature almost identical water dissociation and hydrogen adsorption energies, but evidently different activity trends in alkaline (Ni-MoSe2 ≫ Co-MoSe2 ) and acidic (Co-MoSe2 ≥ Ni-MoSe2 ) media. Experimental and theoretical calculation results demonstrate that tailoring MoSe2 with Ni not only optimizes the hydroxyl adsorption, but also promotes the desorption of OH- and the electron-involved conversion of OHad to OH- , all of which synergistically accelerate the kinetics of OHad + e- ⇄ OH- and thereby the overall kinetics of the alkaline HER.

Solubility-Parameter-Guided Solvent Selection to Initiate Ostwald Ripening for Interior Space-Tunable Structures with Architecture-Dependent Electrochemical Performance.

Despite significant advancement in preparing various hollow structures by Ostwald ripening, one common problem is the intractable uncontrollability of initiating Ostwald ripening due to the complexity of the reaction processes. Here, a new strategy on Hansen solubility parameter (HSP)-guided solvent selection to initiate Ostwald ripening is proposed. Based on this comprehensive principle for solvent optimization, N,N-dimethylformamide (DMF) was screened out, achieving accurate synthesis of interior space-tunable MoSe2 spherical structures (solid, core-shell, yolk-shell and hollow spheres). The resultant MoSe2 structures exhibit architecture-dependent electrochemical performances towards hydrogen evolution reaction and sodium-ion batteries. This pre-solvent selection strategy can effectively provide researchers great possibility in efficiently synthesizing various hollow structures. This work paves a new pathway for deeply understanding Ostwald ripening.

Ligand-engineering Cu-based catalysts to accelerate the electrochemical reduction of CO2.

Two typical Cu-based complex catalysts with piperazine (PR) and p-phenylenediamine (pPDA) ligands were designed to elucidate whether the ligands can tailor the reduction behavior of the Cu species and thus modulate their electrochemical CO2 reduction reaction (eCO2RR) activity. Specifically, Cu-PR underwent a significant in situ transformation into Cu nanoparticles enriched with a Cuδ+/Cu0 interface for high eCO2RR activity, compared to Cu-pPDA. This finding reveals the importance of ligand engineering in modulating the eCO2RR performance of Cu-based complexes.

Tailoring the Atomic-Local Environment of Carbon Nanotube Tips for Selective H2 O2 Electrosynthesis at High Current Densities.

The atomic-local environment of catalytically active sites plays an important role in tuning the activity of carbon-based metal-free electrocatalysts (C-MFECs). However, the rational regulation of the environment is always impeded by synthetic limitations and insufficient understanding of the formation mechanism of the catalytic sites. Herein, the possible cleavage mechanism of carbon nanotubes (CNTs) through the crossing points during ball-milling is proposed, resulting in abundant CNT tips that are more susceptible to be modified by heteroatoms, achieving precise modulation of the atomic environment at the tips. The obtained CNTs with N,S-rich tips (N,S-TCNTs) exhibit a wide potential window of 0.59 V along with H2 O2 selectivity for over 90.0%. Even using air as the O2 source, the flow cell system with N,S-TCNTs catalyst attains high H2 O2 productivity up to 30.37 mol gcat. -1  h-1 @350 mA cm-2 , superior to most reported C-MFECs. From a practical point of view, a solid electrolyzer based on N,S-TCNTs is further employed to realize the in-situ continuous generation of pure H2 O2 solution with high productivity (up to 4.35 mmol cm-2  h-1 @300 mA cm-2 ; over 300 h). The CNTs with functionalized tips hold great promise for practical applications, even beyond H2 O2 generation.

Advances and challenges in metal selenides enabled by nanostructures for electrochemical energy storage applications.

The development of nanomaterials and their related electrochemical energy storage (EES) devices can provide solutions for improving the performance and development of existing EES systems owing to their high electronic conductivity and ion transport and abundant embeddable sites. Recent progress has demonstrated that metal selenides are attracting increasing attention in the field of EES because of their unique structures, high theoretical capacities, rich element resources, and high conductivity. However, there are still many challenges in their application in EES, and thus the use of nanoscale metal selenide materials in commercial devices is limited. In this review, we summarize recent advances in the nanostructured design of metal selenides (e.g., zero-, one-, two-, and three-dimensional, and self-supported structures) and present their advantages in terms of EES performance. Moreover, some remarks on the potential challenges and research prospects of nanostructured metal selenides in the field of EES are presented.

Strain-regulated Gibbs free energy enables reversible redox chemistry of chalcogenides for sodium ion batteries.

Manipulating the reversible redox chemistry of transition metal dichalcogenides for energy storage often faces great challenges as it is difficult to regulate the discharged products directly. Herein we report that tensile-strained MoSe2 (TS-MoSe2) can act as a host to transfer its strain to corresponding discharged product Mo, thus contributing to the regulation of Gibbs free energy change (ΔG) and enabling a reversible sodium storage mechanism. The inherited strain results in lattice distortion of Mo, which adjusts the d-band center upshifted closer to the Fermi level to enhance the adsorbability of Na2Se, thereby leading to a decreased ΔG of the redox chemistry between Mo/Na2Se and MoSe2. Ex situ and in situ experiments revealed that, unlike the unstrained MoSe2, TS-MoSe2 shows a highly reversible sodium storage, along with an evidently improved reaction kinetics. This work sheds light on the study on electrochemical energy storage mechanism of other electrode materials.

Oxygen Vacancies Boosting Lithium-Ion Diffusion Kinetics of Lithium Germanate for High-Performance Lithium Storage.

Oxygen vacancies play a positive role in optimizing the physical and chemical properties of metal oxides. In this work, we demonstrated oxygen vacancy-promoted enhancement of Li-ion diffusion kinetics in Li2GeO3 nanoparticle-encapsulated carbon nanofibers (denoted as Li2GeO3-x/C) and accordingly boosted lithium storage. The introduction of the oxygen vacancies in Li2GeO3-x/C can enhance electronic conductivity and evidently decrease activation energy of Li-ion transport, thus resulting in evidently accelerated Li-ion diffusion kinetics during the lithiation/delithiation process. Thus, the Li2GeO3-x/C nanofibers exhibit an exceptionally large discharge capacity of 1460.5 mA h g-1 at 0.1 A g-1, high initial Coulombic efficiency of 81.3%, and excellent rate capability. This facile and efficient strategy could provide a reference for injecting the oxygen vacancies into other metal oxides for high-performance anode materials.

Co9S8@MoS2 Core-Shell Heterostructures as Trifunctional Electrocatalysts for Overall Water Splitting and Zn-Air Batteries.

The development of efficient non-noble-metal electrocatalysts is of critical importance for clean energy conversion systems, such as fuel cells, metal-air batteries, and water electrolysis. Herein, uniform Co9S8@MoS2 core-shell heterostructures have been successfully prepared via a solvothermal approach, followed by an annealing treatment. Transmission electron microscopy, X-ray absorption near-edge structure, and X-ray photoelectron spectroscopy measurements reveal that the core-shell structure of Co9S8@MoS2 can introduce heterogeneous nanointerface between Co9S8 and MoS2, which can deeply influence its charge state to boost the electrocatalytic performances. Besides, due to the core-shell structure that can promote the synergistic effect of Co9S8 and MoS2 and provide abundant catalytically active sites, Co9S8@MoS2 exhibits a superior hydrogen evolution reaction performance with a small overpotential of 143 mV at 10 mA cm-2 and a small Tafel slope value of 117 mV dec-1 under alkaline solution. Meanwhile, the activity of Co9S8@MoS2 toward oxygen evolution reaction is also impressive with a low operating potential (∼1.57 V vs reversible hydrogen electrode) at 10 mA cm-2. By using Co9S8@MoS2 catalyst for full water splitting, an alkaline electrolyzer affords a cell voltage as low as 1.67 V at a current density of 10 mA cm-2. Also, Co9S8@MoS2 reveals robust oxygen reduction reaction performance, making it an excellent catalyst for Zn-air batteries with a long lifetime (20 h). This work provides a new means for the development of multifunctional electrocatalysts of non-noble metals for the highly demanded electrochemical energy technologies.

Controllable selenium vacancy engineering in basal planes of mechanically exfoliated WSe2 monolayer nanosheets for efficient electrocatalytic hydrogen evolution.

Engineering intrinsic selenium vacancies (Se-vacancies) was achieved in mechanically exfoliated WSe2 monolayer nanosheets (WSe2 MLNSs) via an annealing treatment. Our theoretical and experimental results reveal that these Se-vacancies can efficiently activate and optimize the basal planes of the WSe2 MLNSs. As expected, the optimized catalyst exhibits efficient electrocatalytic hydrogen evolution.