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The single-atomic-site doping of oxophilic-metal (Ru) species in FeCo-LDH leads to the active atom reconstruction at symmetry-breaking interfaces and then the excellent catalytic performance for OER/HER and overall water splitting at large current densities.

Although molybdenum disulfide (MoS2)-based materials are generally known as active electrocatalysts for the hydrogen evolution reaction (HER), the inert performance for the oxygen evolution reaction (OER) seriously limits their wide applications in alkaline electrolyzers due to there exists too strong metal-sulfur (M−S) bond in MoS2. Herein, by means of surface reorganization engineering of bimetal Al, Co-doped MoS2 (devoted as AlCo3-MoS2) through in situ substituting partial oxidation, we successfully significantly activate the OER activity of MoS2, which affords a considerably low overpotential of 323 mV at −30 mA cm−2, far lower than those of MoS2, Al-MoS2 and Co-MoS2 catalysts. Essentially, the AlCo3-MoS2 substrate produces lots of M−O (M=Al, Co and Mo) species with oxygen vacancies, which trigger the surface self-reconstruction of pre-catalysts and simultaneously boost the electrocatalytic OER activity. Moreover, benefiting from the moderate M−O species formed on the surface, the redistribution of surface electron states is induced, thus optimizing the adsorption of OH* and OOH* intermediates on metal oxyhydroxides and awakening the OER activity of MoS2.

Interfacial atomic configuration between dual-metal active species and nitrogen-carbon substrates is of great importance for improving the intrinsic activity of catalysts toward oxygen reduction reaction (ORR). Thus, from the atomic-scale engineering we develop a high intrinsic activity ORR catalyst in terms of incorporating atomically dispersed dual Fe centers (single Fe atoms and ultra-small Fe atomic clusters) into bamboo-like N-doped carbon nanotubes. Benefiting from atomically dispersed dual-Fe centers on the atomic interface of Fe-Nx/carbon nanotubes, the fabricated dual Fe centers catalyst exhibits an extremely high ORR activity (Eonset = 1.006 V; E1/2 = 0.90 V), beyond state-of-the-art Pt/C. Remarkably, this catalyst also shows a superior kinetic current density of 19.690 mA·cm−2, which is 7 times that of state-of-the-art Pt/C. Additionally, based on the excellent catalyst, the primary Zn-air battery reveals a high power density up to 137 mW·cm−2 and sufficient potential cycling stability (at least 25 h). Undoubtedly, given the unique structure-activity relationship of dual-Fe active species and metal-nitrogen-carbon substrates, the catalyst will show great prospects in highly efficient electrochemical energy conversion devices.

The density functional theory calculation results reveal that the adjacent defect concentration and electronic spin state can effectively activate the Co

Introduction of surface defects and phase control engineering in the electrocatalytic system of overall water splitting has played a crucial role in significantly enhancing its electrocatalytic activity toward the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in water splitting, but the relationship between structure and electrocatalysis is still elusive. Herein, we report a solid–liquid method to induce surface reorganization (formation of a chalcogenide layer with rich chalcogenide vacancies) and phase transformation (Co9S8-to-Co3S4) simultaneously on cobalt chalcogenide. Featuring a uniform 2D morphology and the in situ formation of sulfur (S) vacancies, in a 0.1 M KOH solution, it exhibits a low overpotential of 288 mV vs. RHE at 10 mA cm−2, a low Tafel slope of 43.4 mV dec−1, and strong cycling stability (35 h), outperforming commercial RuO2 and most reported OER electrocatalysts. In addition, we also investigate the OER activity of the Co–S–P electrode in 1.0 M KOH solutions. Co0.37S0.38P0.02 NSs only need 257 mV to reach a current density of 10 mA cm−2. Meanwhile, the Tafel slope of Co0.37S0.38P0.02 NSs (44.0 mV dec−1) is lower than those of other recently reported electrocatalysts. Also, it shows high HER electrocatalytic activity in alkaline and acidic solutions. Finally, the Co0.37S0.38P0.02 electrode is used as a cathode and anode simultaneously for overall water splitting, which merely requires a cell voltage of 1.59 V at 10 mA cm−2 with excellent stability (40 h).

The hydrogen evolution reaction (HER) is an ideal model to explore the effect between the activity and the surface vacancy of catalysts. Compared to the anion vacancy, the cation vacancy is more challenging to selectively generate due to the large formation energy, and the serious lack of insight into the structure-activity relationship of cation vacancy-rich catalysts. Herein, we report a facile solid-liquid phase chemical strategy for in situ formation of cation vacancies in a five-fold twinned PtPdRuTe anisotropic structure (v-Pd3Pt29Ru62Te6 AS). Five-fold twinned AS with metal vacancies preferentially produced is confirmed by both X-ray photoelectron spectroscopy (XPS) and high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM). Due to the synergy of metal vacancies and twinned structural advantages, including the appropriate hydrogen binding energy, large exposed surface, anisotropic structure and fast mass/charge transport, v-Pd3Pt29Ru62Te6 AS exhibits significantly enhanced HER electrocatalytic performance in both alkaline and acidic solutions, with ultrasmall overpotentials of 22 and 39 mV to achieve 10 mA cm−2, respectively, and remarkable long-term stability (at least 30 h). These results herald a promising strategy to utilize defective twinned materials for advanced energy storage applications.

The integration of different active sites into metallic catalysts, which may impart new properties and functionalities, is desirable yet challenging. Herein, a novel strategy is demonstrated to integrate atomic vacancies onto a twinned Pd2CoAg surface. This strategy shows that such integration is highly efficient for hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) catalysis at room temperature. We characterize the composition and structure of the twinned Pd2CoAg nanocrystals with vacancy (v-Pd2CoAg NCs) interfaces and it is shown that the Co addition not only increases the atomic vacancies of Pd2Ag twinned interface, but also leads to the formation of oxygen vacancies on the surface of CoOx. The synergistic effect of the surface atomic vacancies and metal twinned interfaces of v-Pd2CoAg NCs can tune the charge-density distribution on the surface of the electrocatalysts, and result in a 5 times increase in ORR mass activity than that of Pt/C at 0.9 V. This study provides a foundation for the rational design of ‘active sites’ for practical HER and ORR electrocatalysts.

The coordination environment of Ru centers determines their catalytic performance, however, much less attention is focused on cluster-induced charge transfer in a Ru single-atom system. Herein, by density functional theory (DFT) calculations, a competitive coordination-pairing between Ru clusters (RuRu bond) and single-atoms (RuO bond) is revealed leading to the charge redistribution between Ru and O atoms in ZnFe

Defect engineering is widely applied in transition metal dichalcogenides to produce high-purity hydrogen. However, the instability of vacancy states on catalysis still remains a considerable challenge. Here, our first-principles calculations showed that, by optimizing the asymmetric S vacancy in the highly asymmetric 1T' crystal of layered bitransition metal dichalcogenides (Co-MoS2) in light of Pd modulation, the relative amount of metastable phase and the quantity of active sites in the structure can be reduced and increased, respectively, leading to a further boosted hydrogen evolution reaction (HER) activity toward layered bi-transition metal dichalcogenides. Thus, we then used a "click" chemistry strategy to make such a catalyst with engineered unsaturated sulfur edges via a strong coupling effect between ultrafine Pd ensembles and Co-MoS2 nanosheets. As expected, the Pd-modulated Co-MoS2 nanosheets exhibited a very low overpotential of 60 mV at 10 mA cm-2 with a small Tafel slope (56 mV dec-1) for the HER in 1.0 M PBS, comparable to those of commercial Pt/C. In addition, their high HER activity was retained in acidic and alkaline conditions. Both the theoretical and experimental results revealed that Pd ensembles can efficiently activate and stabilize the inert basal plane S sites during HER processes as a result of the formation of Pd-S in Co-MoS2. This work not only provides a deeper understanding of the correlation between defect sites and intrinsic HER catalytic properties for transition metal chalcogenide (TMD)-based catalysts, but also offers new insights into better designing earth-abundant HER catalysts displaying high efficiency and durability.

Surface ion vacancy engineering at the atomic scale has attracted much attention to efficiently improve the electrocatalytic activity for the hydrogen evolution reaction (HER). Especially, compared with anion vacancies, cation vacancies are more challenging to generate, and studies on the structure–activity relationship of ion vacancy-rich metal oxide catalysts are still lacking. Herein, by means of abundant dangling unsaturated O and Ru vacancies, we report atomically dispersed MoRu pairs (rGO-MoO3−x–MoRu) stabilized with well-coupled graphene and MoO3−x. The atomically dispersed state of MoRu sites is confirmed by both high-angle annular dark-field scanning TEM (HAADF-STEM) and X-ray absorption fine structure (XAFS) measurements. As a result, rGO-MoO3−x–MoRu pairs show outstanding HER performance with very low overpotentials of 20 and 60 mV at 10 mA cm−2 under alkaline and acidic conditions, and maintain steady hydrogen bubble evolution continuously for 35 h. Meanwhile, for HER activity, they exhibit a positive correlation with the amount of oxygen vacancies, resulting in a favorable change in the adsorption behavior of H atoms on their neighboring Mo or Ru atoms.

Low-cost and highly effective catalysts are crucial to the electrocatalytic hydrogen evolution reaction (HER). Among non-noble catalysts, molybdenum carbides are promising candidates because of their high reserves, stability, low cost, and structural diversity. In this work, we report a simple method to fabricate a hollow porous Mo2C@C nanoball through a hydrothermal preparation process of molybdenum precursors at high temperatures. Specifically, we have combined interfacial polymerization and the chelation effect to synthesize the Mo-polydopamine (Mo-PDA) precursor. As a result, Mo2C@C-3 only requires an ultralow Tafel slope (~55 mV dec−1) and low overpotential (η50 ≈ 167 mV) in a 0.5 M H2SO4 solution with long-term cycling stability. Besides, it also exhibits outstanding activity and stability under extensive HER testing in alkaline media. This study is promising for the development of advanced molybdenum carbide electrocatalysts toward electrochemical applications.

Heteroatom inducement is a possible way to tune the catalytic capability of electrocatalysts in oxygen evolution reaction (OER). In this work, we adopt a facile solid-liquid-phase chemical method to yield hollow Ru-RuPx-CoxP polyhedra. Herein, the in-situ introduced Ru can induce the surface reconstruction of Co2P into Ru-RuPx-CoxP polyhedra due to unstable surface terminations proved by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Line-scan electron energy loss spectroscopy (EELS) analyses. As expected, Ru-RuPx-CoxP with large specific surface area and abundant active sites shows remarkable high OER catalytic activity (η10 = 291 mV) and stability (at least 10000 cycles). DFT calculations further demonstrate that the presence of Ru metal promotes the electrocatalytic reaction kinetics through increasing the density of states at the Fermi level with reduced intermediate adsorption energy and improving electron transfer.

Precisely tuning the geometric and phase structure of noble metal-based heterostructure nanomaterials has been an effective way to induce a metastable defect interface system for the fast hydrogen evolution reaction (HER) kinetics in alkaline media. However, the unstable defect nature of metastable materials hinders their practical applications. Herein, as demonstrated by the theoretical calculation, the optimal Gibbs free energy of adsorbed H2O (ΔGH2O) and water dissociation (ΔGB) can be created for five-fold twinned Ru on Cu NSs with metastable interfaces. Thus, we successfully design and construct an in-situ metastable interface in five-fold twinned Ru supported on vertically oriented Cu nanosheets (Cu NSs) (devoted as CuRux NSs). Among them, CuRu8 NSs display unprecedented overpotentials of 8 and 39 mV at 10 and 100 mA cm−2, respectively. Furthermore, CuRu8 NSs also demonstrate high intrinsic mass activity of 77.528 A g−1 at an overpotential of 20 mV and a large exchange current density of 5.014 mA cm−2, with outstanding stability (almost no activity degradation for 130 h). These represent one of the best alkaline HER catalysts to date for Ru-based catalysts. Importantly, CuRu8 NSs possess nearly 100% Faradaic yield, confirming the high selectivity toward hydrogen evolution reaction. Furthermore, the fine structural analysis evidences that the in-situ incorporated five-fold twinned Ru nanoparticles coupled electronically with Cu NSs not only avoid migration and aggregation of the metal particles, but also effectively promote the formation of heterostructure nanosheet arrays with abundant active sites, enhancing the alkaline hydrogen evolution kinetics.

The surface configuration of low‐cost spinel oxides for oxygen evolution reaction (OER) can significantly affect the electrochemical behavior by generating a thin oxyhydroxide layer and other structures on the surface. Herein, we design and construct phosphorus (P)-activated ~1.0 nm ultrathin CoO nanosheets (devoted as Px-CoO NSs) with enriched P-O bonds and high valence state Co active sites, which is beneficial to the OER process due to the balance with Co3+ and oxygen vacancies on the reconstructed surface/interface. In addition, such an ultrathin nanosheet structure is also benefit to expose more active sites and improve the intrinsic electronic conductivity. As a result, the surface reconstructed Px-CoO NSs show superior OER activity compared with pure CoO and IrO2 as benchmark. Furthermore, P1-CoO NSs demonstrate intrinsically high mass activity of 6.8 A gCo−1 at an overpotential of 270 mV, large turnover frequency of 0.0024 s−1 at an overpotential of 300 mV, and strong cycling stability in 0.1 M KOH solutions. Structural analysis further reveals that, as compared with CoO, the P-substitution not only induces the surface reconstruction into active Co oxyhydroxides under OER conditions, but also enhances the reaction kinetics. Undoubtedly, this work enriches the ways to prepare high-performance transition-metal-oxide-based catalyst for practical applications.

Developing high-efficiency electrocatalysts is the key to generating and consuming hydrogen by accelerating the reaction kinetics of the hydrogen oxidation and evolution reactions (HOR/HER). Although the kinetics process of the adsorbed intermediates (Had)-water-oxophilic metal has been investigated in the alkaline media, the hydroxyl species (Had or OH- or OHad)-activity relationship for oxophilic metal alloy electrocatalysis during multiple HOR and HER processes is still unclear. In this regard, our density functional theory (DFT) calculation results show that, due to partial substitution of Ru (Rh) clusters at buried interfaces by oxophilic-metal (OM) species, the long-range order of Ru (Rh) clusters surface atoms can be broken, and then the active atom reconstruction at buried interfaces is triggered, which decreases the oxidation intermediates of Ru (Rh) and gives rise to the increased activity for alkaline HER/HOR. At the same time, an OH--adsorption promoter forms, also favorable for OER. Encouraged by the first-principles calculation results, an ultralow-loaded OM species (0.13 wt% Co, 0.23 wt% Mn, 2.4 wt% Cr or 1.3 wt% Fe) incorporated RuRh cluster (RuRh-OM) catalyst is built by a mixed-solvent strategy. Impressively, after incorporating OM (Co; Mn; Cr and Fe), these catalysts exhibit higher HOR activity than pristine RuRh and commercial Pt even at higher potentials in 0.1 M KOH solutions, which outperforms most reported HOR catalysts and ~ 2 times higher than that of commercial Pt. Meanwhile, RuRh-Co also exhibits the highest HER activity among all reported Ru-based HER catalysts, and greatly improved OER and overall water spitting performances in alkaline solutions (1 M KOH for HER and overall water spitting, 0.1 M KOH for OER), exceeding RuRh and commercial noble metal catalysts.

Engineering the 2D metal-organic framework (MOF) material can enrich the metal-unsaturated edges as active sites for catalysis, however, introducing multiple heterointerfaces and vacancy defects into 2D MOF and exploring their effects on electrocatalytic oxygen evolution reaction (OER) remain a major challenge. Here we construct ultrathin and highly curved 2D FeCoNi trimetal-organic framework nanosheets (FeCoNi-MOFs) with only approximately 1.5 nm thickness and abundant oxygen vacancies. The formed defect-rich FeCoNi-MOFs display outstanding OER performance with a much smaller overpotential of 254 mV at 10 mA cm−2 and remarkable stability for over 100 h in alkaline solutions. This is the highest OER activity level attained for direct-MOF catalysts. Theoretical analysis of FeCoNi MOFs with rich oxygen vacancies further suggests that the increased Fermi level with multiple heterointerfaces and the addition of oxygen vacancies co-facilitate the pre-oxidation of low-valence metals and the reconstruction/deprotonation of intermediate metal−OOH, thus enhancing electron transport efficiency.

Developing bifunctional catalysts for both the hydrogen evolution reaction (HER) and the oxygen reduction reaction (ORR) is crucial for obtaining hydrogen easily by water splitting to promote electrochemical energy conversion in fuel cells. In this paper, we report a facile approach for the synthesis of Pd nanoparticle assemblies (NPAs) with porous structure as catalysts for both the HER and the ORR with desirable electrocatalytic activities and long-term stability. For the HER, the porous Pd NPAs exhibit a low onset potential, a small Tafel slope of 30 mV dec–1, and an exceptionally low overpotential of about 80 mV at a current density of 100 mA cm–2, and these porous Pd NPAs maintain their catalytic activity for at least 1000 cyclic voltammetry (CV) cycles of durability in 0.5 m H2SO4. As for the ORR, the porous Pd NPAs offer a remarkable catalytic activity with a diffusion-limiting current density of 3.85 mA cm–2, a half-potential of 0.837 V, and an onset potential of 0.926 V at 1600 rpm with a scan rate of 5 mV s–1. This study enables the design of novel bifunctional electrocatalysts in the renewable energy field.

Electrocatalysis of the hydrogen evolution reaction (HER) is a vital and demanding, yet challenging, task to produce clean energy applications. Here, the RuRh2 bimetallene nanoring with rich structural defects is designed and successfully synthesized by a mixed‐solvent strategy, displaying ascendant HER performance with high mass activity at −0.05 and −0.07 V, separately higher than that of the commercial Pt catalyst. Also, it maintains steady hydrogen bubble evolution even after 30 000 potential cycles in acid media. Furthermore, the RuRh2 bimetallene nanoring shows an outstanding activity in both alkaline and neutral media, outperforming that of Pt catalysts and other reported HER catalysts. A combination of atomic‐scale structure observation and density functional theory calculations demonstrates that both the grain boundaries and symmetry breaking of RuRh2 bimetallene cannot only weaken the adsorption strength of atomic hydrogen, but also facilitate the transfer of electrons and the adsorption of reactants, further boosting the HER electrocatalytic performance in all pH values., Theoretical calculation results demonstrate that both the grain boundaries and atomic configurations of RuRh bimetallene can introduce more active sites via the symmetry breaking caused by atom displacements. Accordingly, RuRh bimetallene nanorings are designed and successfully synthesized by a mixed‐solvent strategy, displaying superior activity and stability for the hydrogen evolution reaction (HER) in all pH values.

Developing OER&ORR bifunctional electrocatalysts has great significance for promoting the green energy conversion and storage technologies. Herein, nitrogen doped carbon coupled FeNi3 intermetallic compound (FeNi3@NC) is designed and constructed by a super facile route. Rich defects, multiple active centers and strong synergistic effect allow FeNi3@NC with superior OER&ORR performance in alkaline environments. It exhibits an ultralow overpotential (Eover) of 277 mV at 10 mA/cm2 for OER, and a high half-wave potential (E1/2) of 0.86 V for ORR which outperform commercial Pt/C electrocatalysts. As a result, the ΔE (ΔE = Eover,OER – E1/2,ORR) value of 0.65 V largely surpasses Pt/C-IrO2 noble metal benchmarks (ΔE = 0.73 V). Furthermore, density function theory calculations are performed to probe its electrocatalytic mechanism. As expected, the peak power density and energy density of FeNi3@NC based rechargeable Zn-air battery reaches 139 mW/cm2 at 234 mA/cm2 and 915 Wh kg−1 at 10 mA/cm2, respectively, with excellent stability. Our exploration provides a guideline for synthesis of advanced bifunctional electrocatalyst.

Oxygen vacancies (Ovac) can improve electrocatalytic activities in the oxygen evolution reaction (OER) process but remain a great challenge. Herein, we report a facile two-step approach to synthesizing La-doped CoOx nanosheets (NSs) with abundant oxygen vacancies by a La-triggered effect. Profiting from enriched Ovac and fast charge transfer, La-doped CoOx NSs deliver a remarkably high OER activity with a low overpotential of 353 mV at 10.0 mA cm−2 and a Tafel slope of 78.2 mV dec−1, surpassing those of initial CoOx, IrO2, and most reported non-noble metal based electrocatalysts. In addition, they also exhibit superior durability with only slight degradation after continuous operation of 35 h in a 0.1 M KOH solution. Undoubtedly, the results inspire the use of La into the oxygen vacancies to explore highly active catalysts for various applications.