2D Ruthenium-Chromium Oxide with Rich Grain Boundaries Boosts Acidic Oxygen Evolution Reaction Kinetics.

Ruthenium oxide is currently considered as the promising alternative to Ir-based catalysts employed for proton exchange membrane water electrolyzers but still faces the bottlenecks of limited durability and slow kinetics. Herein, a 2D amorphous/crystalline heterophase ac-Cr0.53Ru0.47O2-δ substitutional solid solution with pervasive grain boundaries (GBs) is developed to accelerate the kinetics of acidic oxygen evolution reaction (OER) and extend the long-term stability simultaneously. The ac-Cr0.53Ru0.47O2-δ shows a super stability with a slow degradation rate and a remarkable mass activity of 455 A gRu -1 at 1.6 V vs RHE, which is ≈3.6- and 5.9-fold higher than those of synthesized RuO2 and commercial RuO2, respectively. The strong interaction of Cr-O-Ru local units in synergy with the specific 2D structural characteristics of ac-Cr0.53Ru0.47O2-δ dominates its enhanced stability. Meanwhile, high-density GBs and the shortened Ru-O bonds tailored by amorphous/crystalline structure and Cr-O-Ru interaction regulate the adsorption and desorption rates of oxygen intermediates, thus accelerating the overall acidic OER kinetics.

Synergistic Effect of Grain Boundaries and Oxygen Vacancies on Enhanced Selectivity for Electrocatalytic CO2 Reduction.

Dual-engineering involved of grain boundaries (GBs) and oxygen vacancies (VO) efficiently engineers the material's catalytic performance by simultaneously introducing favorable electronic and chemical properties. Herein, a novel SnO2 nanoplate is reported with simultaneous oxygen vacancies and abundant grain boundaries (V,G-SnOx/C) for promoting the highly selective conversion of CO2 to value-added formic acid. Attributing to the synergistic effect of employed dual-engineering, the V,G-SnOx/C displays highly catalytic selectivity with a maximum Faradaic efficiency (FE) of 87% for HCOOH production at -1.2 V versus RHE and FEs > 95% for all C1 products (CO and HCOOH) within all applied potential range, outperforming current state-of-the-art electrodes and the amorphous SnOx/C. Theoretical calculations combined with advanced characterizations revealed that GB induces the formation of electron-enriched Sn site, which strengthens the adsorption of *HCOO intermediate. While GBs and VO synergistically lower the reaction energy barrier, thus dramatically enhancing the intrinsic activity and selectivity toward HCOOH.

Switching Product Selectivity in CO2 Electroreduction via Cu-S Bond Length Variation.

Regulating competitive reaction pathways to direct the selectivity of electrochemical CO2 reduction reaction toward a desired product is crucial but remains challenging. Herein, switching product from HCOOH to CO is achieved by incorporating Sb element into the CuS, in which the Cu-S ionic bond is coupled with S-Sb covalent bond through bridging S atoms that elongates the Cu-S bond from 2.24 Å to 2.30 Å. Consequently, CuS with a shorter Cu-S bond exhibited a high selectivity for producing HCOOH, with a maximum Faradaic efficiency (FE) of 72%. Conversely, Cu3SbS4 characterized by an elongated Cu-S bond exhibited the most pronounced production of CO with a maximum FE of 60%. In situ spectroscopy combined with density functional theory calculations revealed that the altered Cu‒S bond length and local coordination environment make the *HCOO binding energy weaker on Cu3SbS4 compared to that on CuS. Notably, a volcano-shaped correlation between the Cu-S bond length and adsorption strength of *COOH indicates that Cu-S in Cu3SbS4 as double-active sites facilitates the adsorption of *COOH, and thus results in the high selectivity of Cu3SbS4 toward CO.

Substantial Impact of Built-in Electric Field and Electrode Potential on the Alkaline Hydrogen Evolution Reaction of Ru-CoP Urchin Arrays.

Although great efforts on the delicate construction of a built-in electric field (BIEF) to modify the electronic properties of active sites have been conducted, the substantial impact of BIEF coupled with electrode potential on the electrochemical reactions has not been clearly investigated. Herein, we designed an alkaline hydrogen evolution reaction (HER) catalyst composed of heterogeneous Ru-CoP urchin arrays on carbon cloth (Ru-CoP/CC) with a strong BIEF with the guidance of density functional theory (DFT) calculations. Impressively, despite its unsatisfactory activity at 10 mA cm-2 (overpotential of 44 mV), Ru-CoP/CC exhibited better activity (357 mV) than the benchmark Pt/C catalyst (505 mV) at 1 A cm-2 . Experimental and theoretical studies revealed that strong hydrogen adsorption on the interfacial Ru atoms created a high energy barrier for hydrogen desorption and spillover, resulting in unsatisfactory activity at low current densities. However, as the electrode potential became more negative (i.e., the current density increased), the barrier for hydrogen spillover from the interfacial Ru to the Co site, which had near-zero hydrogen adsorption energy, significantly decreased, thus greatly accelerating the whole alkaline HER process. This explains why the activity of Ru-CoP is relatively susceptible to the electrode potential compared to Pt/C.

Grain Boundary Tailors the Local Chemical Environment on Iridium Surface for Alkaline Electrocatalytic Hydrogen Evolution.

Even though grain boundaries (GBs) have been previously employed to increase the number of active catalytic sites or tune the binding energies of reaction intermediates for promoting electrocatalytic reactions, the effect of GBs on the tailoring of the local chemical environment on the catalyst surface has not been clarified thus far. In this study, a GBs-enriched iridium (GB-Ir) was synthesized and examined for the alkaline hydrogen evolution reaction (HER). Operando Raman spectroscopy and density functional theory (DFT) calculations revealed that a local acid-like environment with H3 O+ intermediates was created in the GBs region owing to the electron-enriched surface Ir atoms at the GBs. The H3 O+ intermediates lowered the energy barrier for water dissociation and provided enough hydrogen proton to promote the generation of hydrogen spillover from the sites at the GBs to the sites away from the GBs, thus synergistically enhancing the hydrogen evolution activity. Notably, the GB-Ir catalyst exhibited a high alkaline HER activity (10 mV @ 10 mA cm-2 , 20 mV dec-1 ). We believe that our findings will promote further research on GBs and the surface science of electrochemical reactions.

Constructing Interfacial Oxygen Vacancy and Ruthenium Lewis Acid-Base Pairs to Boost the Alkaline Hydrogen Evolution Reaction Kinetics.

Simultaneous optimization of the energy level of water dissociation, hydrogen and hydroxide desorption is the key to achieving fast kinetics for the alkaline hydrogen evolution reaction (HER). Herein, the well-dispersed Ru clusters on the surface of amorphous/crystalline CeO2-δ (Ru/ac-CeO2-δ ) is demonstrated to be an excellent electrocatalyst for significantly boosting the alkaline HER kinetics owing to the presence of unique oxygen vacancy (VO ) and Ru Lewis acid-base pairs (LABPs). The representative Ru/ac-CeO2-δ exhibits an outstanding mass activity of 7180 mA mgRu -1 that is approximately 9 times higher than that of commercial Pt/C at the potential of -0.1 V (V vs RHE) and an extremely low overpotential of 21.2 mV at a geometric current density of 10 mA cm-2 . Experimental and theoretical studies reveal that the VO as Lewis acid sites facilitate the adsorption of H2 O and cleavage of H-OH bonds, meanwhile, the weak Lewis basic Ru clusters favor for the hydrogen desorption. Importantly, the desorption of OH from VO sites is accelerated via a water-assisted proton exchange pathway, and thus boost the kinetics of alkaline HER. This study sheds new light on the design of high-efficiency electrocatalysts with LABPs for the enhanced alkaline HER.

Tuning Proton Insertion Chemistry for Sustainable Aqueous Zinc-Ion Batteries.

Rechargeable aqueous zinc-ion batteries (ZIBs) have emerged as an alternative to lithium-ion batteries due to their affordability and high level of safety. However, their commercialization is hindered by the low mass loading and irreversible structural changes of the cathode materials during cycling. Here, a disordered phase of a manganese nickel cobalt dioxide cathode material derived from wastewater via a coprecipitation process is reported. When used as the cathode for aqueous ZIBs , the developed electrode delivers 98% capacity retention at a current density of 0.1 A g-1 and 72% capacity retention at 1 A g-1 while maintaining high mass loading (15 mg cm-2 ). The high performance is attributed to the structural stability of the Co and Ni codoped phase; the dopants effectively suppress Jahn-Teller distortion of the manganese dioxide during cycling, as revealed by operando X-ray absorption spectroscopy. Also, it is found that the Co and Ni co-doped phase effectively inhibits the dissolution of Mn2+ , resulting in enhanced durability without capacity decay at first 20 cycles. Further, it is found that the performance of the electrode is sensitive to the ratio of Ni to Co, providing important insight into rational design of more efficient cathode materials for low-cost, sustainable, rechargeable aqueous ZIBs.

Boosting Hydrogen Evolution Reaction by Phase Engineering and Phosphorus Doping on Ru/P-TiO2.

Synergistic optimization of the elementary steps of water dissociation and hydrogen desorption for the hydrogen evolution reaction (HER) in alkaline media is a challenge. Herein, the Ru cluster anchored on a trace P-doped defective TiO2 substrate (Ru/P-TiO2 ) was synthesized as an electrocatalyst for the HER; it exhibited a commercial Pt/C-like geometric activity and an excellent mass activity of 9984.3 mA mgRu -1 at -0.05 V vs. RHE, which is 34.3 and 18.7 times higher than that of Pt/C and Ru/TiO2 , respectively. Experimental and theoretical studies indicated that using a rutile-TiO2 -crystal-phase substrate enhanced the HER activity more than the anatase phase. Rich surface oxygen vacancies on rutile-TiO2 facilitated the adsorption and dissociation of water, while the partial substitution of Ti4+ with P5+ enhanced H2 generation by facilitating hydrogen spillover from the Ru site to the surface P site, synergistically enhancing the HER activity.

Sodium-Decorated Amorphous/Crystalline RuO2 with Rich Oxygen Vacancies: A Robust pH-Universal Oxygen Evolution Electrocatalyst.

The oxygen evolution reaction (OER) is a key reaction for many electrochemical devices. To date, many OER electrocatalysts function well in alkaline media, but exhibit poor performances in neutral and acidic media, especially the acidic stability. Herein, sodium-decorated amorphous/crystalline RuO2 with rich oxygen vacancies (a/c-RuO2 ) was developed as a pH-universal OER electrocatalyst. The a/c-RuO2 shows remarkable resistance to acid corrosion and oxidation during OER, which leads to an extremely high catalytic stability, as confirmed by a negligible overpotential increase after continuously catalyzing OER for 60 h at pH=1. Besides, a/c-RuO2 also exhibits superior OER activities to commercial RuO2 and most reported OER catalysts under all pH conditions. Theoretical calculations indicated that the introduction of Na dopant and oxygen vacancy in RuO2 weakens the adsorption strength of the OER intermediates by engineering the d-band center, thereby lowering the energy barrier for OER.

The Heterostructure of Ru2 P/WO3 /NPC Synergistically Promotes H2 O Dissociation for Improved Hydrogen Evolution.

Facilitating the dissociation of water and desorption of hydrogen are both crucial challenges for improving the hydrogen evolution reaction (HER) in alkaline media. Herein, we report the synthesis of heterostructure of Ru2 P/WO3 @NPC (N, P co-doped carbon) by a simple hydrothermal reaction using ruthenium and tungsten salts as precursors, followed by pyrolyzing under an Ar atmosphere. The Ru2 P/WO3 @NPC electrocatalyst exhibits an outstanding HER activity with an overpotential of 15 mV at a current density of 10 mA cm-2 and excellent durability in a 1.0 M KOH solution, outperforming state-of-the-art Pt/C and most reported electrocatalysts. Experimental results combined with density functional calculations reveal that the electron density redistribution in Ru2 P/WO3 @NPC is achieved by electron transfer from NPC to Ru2 P/WO3 and from Ru2 P to WO3 , which directly promotes the dissociation of water on W sites in WO3 and desorption of hydrogen on Ru sites in Ru2 P.

Antimony-Based Composites Loaded on Phosphorus-Doped Carbon for Boosting Faradaic Efficiency of the Electrochemical Nitrogen Reduction Reaction.

A nanocomposite of PC/Sb/SbPO4 (PC, phosphorus-doped carbon) exhibits a high activity and an excellent selectivity for efficient electrocatalytic conversion of N2 to NH3 in both acidic and neutral electrolytes under ambient conditions. At a low reductive potential of -0.15 V versus the reversible hydrogen electrode (RHE), the PC/Sb/SbPO4 catalyst achieves a high Faradaic efficiency (FE) of 31 % for ammonia production in 0.1 m HCl under mild conditions. In particular, a remarkably high FE value of 34 % is achieved at a lower reductive potential of -0.1 V (vs. RHE) in a 0.1 m Na2 SO4 solution, which is better than most reported electrocatalysts towards the nitrogen reduction reaction (NRR) in neutral electrolyte under mild conditions. The change in surface species and electrocatalytic performance before and after N2 reduction is explored by an ex situ method. PC and SbPO4 are both considered as the active species that enhanced the performance of NRR.

Intrabasal Plane Defect Formation in NiFe Layered Double Hydroxides Enabling Efficient Electrochemical Water Oxidation.

Defect engineering has proven to be one of the most effective approaches for the design of high-performance electrocatalysts. Current methods to create defects typically follow a top-down strategy, cutting down the pristine materials into fragmented pieces with surface defects yet also heavily destroying the framework of materials that imposes restrictions on the further improvements in catalytic activity. Herein, we describe a bottom-up strategy to prepare free-standing NiFe layered double hydroxide (LDH) nanoplatelets with abundant internal defects by controlling their growth behavior in acidic conditions. Our best-performing nanoplatelets exhibited the lowest overpotential of 241 mV and the lowest Tafel slope of 43 mV/dec for the oxygen evolution reaction (OER) process, superior to the pristine LDHs and other reference cation-defective LDHs obtained by traditional etching methods. Using both material characterization and density functional theory (DFT) simulation has enabled us to develop relationships between the structure and electrochemical properties of these catalysts, suggesting that the enhanced electrocatalytic activity of nanoplatelets mainly results from their defect-abundant structure and stable layered framework with enhanced exposure of the (001) surface.

Characterization of arsenite (As(III)) and arsenate (As(V)) sorption on synthetic siderite spherules under anoxic conditions: Different sorption behaviors with crystal size and arsenic species.

Arsenite (As(III)) and arsenate (As(V)) uptake by synthesized small- and large-sized siderites (S-siderite and l-siderite) and the effects of crystal size on arsenic sorption were investigated under extremely anoxic and neutral pH conditions. Both siderites exhibited spherical growth mechanism with an inverse relationship between crystal size and specific surface area (SSA). The maximum adsorption capacities normalized to SSA (qm,nor) of S-siderite and l-siderite were 0.161 and 0.174 mg/m2 for As(III), and 1.460 and 0.360 mg/m2 for As(V), respectively, indicating that the sorption affinity of S-siderite depends more on the arsenic species (III and V). Extended X-ray absorption fine structure (EXAFS) revealed that without oxidation change, As(V) adsorbed on both siderites forms inner-sphere complexes through bidentate-binuclear corner-sharing. In contrast, outer-sphere and inner-sphere complexes are formed for As(III) adsorbed on these siderites. In addition, the highest sorption affinity for As(V) uptake by S-siderite is attributed to the precipitation of symplesite (FeII3(AsVO4)2·8H2O), whereas the lowest sorption affinity for As(III) uptake by S-siderite was due to bicarbonates generated by the faster dissolution of S-siderite competing for sorption sites. Our findings suggest that arsenic sorption behaviors and mechanisms are strongly dependent on the arsenic species and the crystal size of siderite.

Atomically Thin Holey Two-Dimensional Ru2P Nanosheets for Enhanced Hydrogen Evolution Electrocatalysis.

The defect engineering of low-dimensional nanostructured materials has led to increased scientific efforts owing to their high efficiency concerning high-performance electrocatalysts that play a crucial role in renewable energy technologies. Herein, we report an efficient methodology for fabricating atomically thin, holey metal-phosphide nanosheets with excellent electrocatalyst functionality. Two-dimensional, subnanometer-thick, holey Ru2P nanosheets containing crystal defects were synthesized via the phosphidation of monolayer RuO2 nanosheets. Holey Ru2P nanosheets exhibited superior electrocatalytic activity for the hydrogen evolution reaction (HER) compared to that exhibited by nonholey Ru2P nanoparticles. Further, holey Ru2P nanosheets exhibited overpotentials of 17 and 26 mV in acidic and alkaline electrolytes, respectively. Thus, they are among the best-performing Ru-P-based HER catalysts reported to date. In situ spectroscopic investigations indicated that the holey nanosheet morphology enhanced the accumulation of surface hydrogen through the adsorption of protons and/or water, resulting in an increased contribution of the Volmer-Tafel mechanism toward the exceptional HER activity of these ultrathin electrocatalysts.

The synergistic effect of Hf-O-Ru bonds and oxygen vacancies in Ru/HfO2 for enhanced hydrogen evolution.

Ru nanoparticles have been demonstrated to be highly active electrocatalysts for the hydrogen evolution reaction (HER). At present, most of Ru nanoparticles-based HER electrocatalysts with high activity are supported by heteroatom-doped carbon substrates. Few metal oxides with large band gap (more than 5 eV) as the substrates of Ru nanoparticles are employed for the HER. By using large band gap metal oxides substrates, we can distinguish the contribution of Ru nanoparticles from the substrates. Here, a highly efficient Ru/HfO2 composite is developed by tuning numbers of Ru-O-Hf bonds and oxygen vacancies, resulting in a 20-fold enhancement in mass activity over commercial Pt/C in an alkaline medium. Density functional theory (DFT) calculations reveal that strong metal-support interaction via Ru-O-Hf bonds and the oxygen vacancies in the supported Ru samples synergistically lower the energy barrier for water dissociation to improve catalytic activities.

Coiled Conformation Hollow Carbon Nanosphere Cathode and Anode for High Energy Density and Ultrafast Chargeable Hybrid Energy Storage.

Lithium-ion batteries and pseudocapacitors are nowadays popular electrochemical energy storage for many applications, but their cathodes and anodes are still limited to accommodate rich redox ions not only for high energy density but also sluggish ion diffusivity and poor electron conductivity, hindering fast recharge. Here, we report a strategy to realize high-capacity/high-rate cathode and anode as a solution to this challenge. Multiporous conductive hollow carbon (HC) nanospheres with microporous shells for high capacity and hollow cores/mesoporous shells for rapid ion transfer are synthesized as cathode materials using quinoid:benzenoid (Q:B) unit resins of coiled conformation, leading to ∼5-fold higher capacities than benzenoid:benzenoid resins of linear conformation. Also, Ge-embedded Q:B HC nanospheres are derived as anode materials. The atomic configuration and energy storage mechanism elucidate the existence of mononuclear GeOx units giving ∼7-fold higher ion diffusivity than bulk Ge while suppressing volume changes during long ion-insertion/desertion cycles. Moreover, hybrid energy storage with a Q:B HC cathode and Ge-Q:B HC anode exploit the advantages of capacitor-type cathode and battery-type anode electrodes, as exhibited by battery-compatible high energy density (up to 285 Wh kg-1) and capacitor-compatible ultrafast rechargeable power density (up to 22 600 W kg-1), affording recharge within a minute.

Exploring the Dominant Role of Atomic- and Nano-Ruthenium as Active Sites for Hydrogen Evolution Reaction in Both Acidic and Alkaline Media.

Ru nanoparticles (NPs) and single atoms (SAs)-based materials have been investigated as alternative electrocatalysts to Pt/C for hydrogen evolution reaction (HER). Exploring the dominant role of atomic- and nano-ruthenium as active sites in acidic and alkaline media is very necessary for optimizing the performance. Herein, an electrocatalyst containing both Ru SAs and NPs anchored on defective carbon (RuSA+NP /DC) has been synthesized via a Ru-alginate metal-organic supramolecules conversion method. RuSA+NP /DC exhibits low overpotentials of 16.6 and 18.8 mV at 10 mA cm-2 in acidic and alkaline electrolytes, respectively. Notably, its mass activities are dramatically improved, which are about 1.1 and 2.4 times those of Pt/C at an overpotential of 50 mV in acidic and alkaline media, respectively. Theoretical calculations reveal that Ru SAs own the most appropriate H* adsorption strength and thus, plays a dominant role for HER in acid electrolyte, while Ru NPs facilitate the dissociation of H2 O that is the rate-determining step in alkaline electrolyte, leading to a remarkable HER activity.

Lattice-Oxygen-Stabilized Li- and Mn-Rich Cathodes with Sub-Micrometer Particles by Modifying the Excess-Li Distribution.

In recent years, Li- and Mn-rich layered oxides (LMRs) have been vigorously explored as promising cathodes for next-generation, Li-ion batteries due to their high specific energy. Nevertheless, their actual implementation is still far from a reality since the trade-off relationship between the particle size and chemical reversibility prevents LMRs from achieving a satisfactory, industrial energy density. To solve this material dilemma, herein, a novel morphological and structural design is introduced to Li1.11 Mn0.49 Ni0.29 Co0.11 O2 , reporting a sub-micrometer-level LMR with a relatively delocalized, excess-Li system. This system exhibits an ultrahigh energy density of 2880 Wh L-1 and a long-lasting cycle retention of 83.1% after the 100th cycle for 45 °C full-cell cycling, despite its practical electrode conditions. This outstanding electrochemical performance is a result of greater lattice-oxygen stability in the delocalized excess-Li system because of the low amount of highly oxidized oxygen ions. Geometric dispersion of the labile oxygen ions effectively suppresses oxygen evolution from the lattice when delithiated, eradicating the rapid energy degradation in a practical cell system.

Building High-Rate Nickel-Rich Cathodes by Self-Organization of Structurally Stable Macrovoid.

Nickel-rich materials, as a front-running cathode for lithium-ion batteries suffer from inherent degradation issues such as inter/intragranular cracks and phase transition under the high-current density condition. Although vigorous efforts have mitigated these current issues, the practical applications are not successfully achieved due to the material instability and complex synthesis process. Herein, a structurally stable, macrovoid-containing, nickel-rich material is developed using an affordable, scalable, and one-pot coprecipitation method without using surfactants/etching agents/complex-ion forming agents. The strategically developed macrovoid-induced cathode via a self-organization process exhibits excellent full-cell rate capability, cycle life at discharge rate of 5 C, and structural stability even at the industrial electrode conditions, owing to the fast Li-ion diffusion, the internal macrovoid acting as "buffer zones" for stress relief, and highly stable nanostructure around the void during cycling. This strategy for nickel-rich cathodes can be viable for industries in the preparation of high-performance lithium-ion cells.

Fe, Al-co-doped NiSe2 nanoparticles on reduced graphene oxide as an efficient bifunctional electrocatalyst for overall water splitting.

Developing low-cost and highly efficient electrocatalysts for overall water splitting is of far-reaching significance for new energy conversion. Herein, dual-cation Fe, Al-co-doped NiSe2 nanoparticles on reduced graphene oxide (Fe, Al-NiSe2/rGO) were prepared as a bifunctional electrocatalyst for overall water splitting. The dual-cation doping can induce a stronger electronic interaction between the foreign atoms and host catalyst, for optimizing the adsorption energy of reaction intermediates. Meanwhile, the leaching out of Al from the crystal structure of the target product during the alkaline wash creates more defects and increases the active site exposure. As a result, the Fe, Al-NiSe2/rGO catalyst exhibits excellent catalytic activities for both the OER and HER with an overpotential of 272 mV @η10 for the OER in 1.0 M KOH and 197 mV @η10 for the HER in 0.5 M H2SO4, respectively. A two-electrode electrolyzer using Fe, Al-NiSe2/rGO as the anode and cathode shows a low voltage of 1.70 V at the current density of 10 mA cm-2. This study emphasizes the synergistic contribution of the dual-cation co-doping effect and more defects created by Al leaching to boost the performance of water splitting.