Strain-modulated Ru-O Covalency in Ru-Sn Oxide Enabling Efficient and Stable Water Oxidation in Acidic Solution.

RuO2 is one of the benchmark electrocatalysts used as the anode material in proton exchange membrane water electrolyser. However, its long-term stability is compromised due to the participation of lattice oxygen and metal dissolution during oxygen evolution reaction (OER). In this work, weakened covalency of Ru-O bond was tailored by introducing tensile strain to RuO6 octahedrons in a binary Ru-Sn oxide matrix, prohibiting the participation of lattice oxygen and the dissolution of Ru, thereby significantly improving the long-term stability. Moreover, the tensile strain also optimized the adsorption energy of intermediates and boosted the OER activity. Remarkably, the RuSnOx electrocatalyst exhibited excellent OER activity in 0.1 M HClO4 and required merely 184 mV overpotential at a current density of 10 mA cm-2 . Moreover, it delivered a current density of 10 mA cm-2 for at least 150 h with negligible potential increase. This work exemplifies an effective strategy for engineering Ru-based catalysts with extraordinary performance toward water splitting.

Hydrogen Spillover-Bridged Volmer/Tafel Processes Enabling Ampere-Level Current Density Alkaline Hydrogen Evolution Reaction under Low Overpotential.

Water-alkaline electrolysis holds a great promise for industry-scale hydrogen production but is hindered by the lack of enabling hydrogen evolution reaction electrocatalysts to operate at ampere-level current densities under low overpotentials. Here, we report the use of hydrogen spillover-bridged water dissociation/hydrogen formation processes occurring at the synergistically hybridized Ni3S2/Cr2S3 sites to incapacitate the inhibition effect of high-current-density-induced high hydrogen coverage at the water dissociation site and concurrently promote Volmer/Tafel processes. The mechanistic insights critically important to enable ampere-level current density operation are depicted from the experimental and theoretical studies. The Volmer process is drastically boosted by the strong H2O adsorption at Cr5c sites of Cr2S3, the efficient H2O* dissociation via a heterolytic cleavage process (Cr5c-H2O* + S3c(#) → Cr5c-OH* + S3c-H#) on the Cr5c/S3c sites in Cr2S3, and the rapid desorption of OH* from Cr5c sites of Cr2S3 via a new water-assisted desorption mechanism (Cr5c-OH* + H2O(aq) → Cr5c-H2O* + OH-(aq)), while the efficient Tafel process is achieved through hydrogen spillover to rapidly transfer H# from the synergistically located H-rich site (Cr2S3) to the H-deficient site (Ni3S2) with excellent hydrogen formation activity. As a result, the hybridized Ni3S2/Cr2S3 electrocatalyst can readily achieve a current density of 3.5 A cm-2 under an overpotential of 251 ± 3 mV in 1.0 M KOH electrolyte. The concept exemplified in this work provides a useful means to address the shortfalls of ampere-level current-density-tolerant Hydrogen evolution reaction (HER) electrocatalysts.

Effects of compositional engineering and surface passivation on the properties of halide perovskites: a theoretical understanding.

Halide perovskite solar cells have demonstrated high power conversion efficiency. Compositional engineering and surface passivation technologies have been drawing great attention to enhance their energy conversion efficiency and moisture resistance. In this study, the density functional theory method was employed to understand the effects of compositional engineering at the A site of perovskites and the 3-butenoic acid-based passivation layer on the structural, electronic and optical properties of halide perovskites. Our results suggest that the electronic and optical properties of CsPbI3 can be tuned by the mixing of caesium and FA cations. Moreover, the calculation of adsorption energies on mixed-cation Cs1-xFAxPbI3(001) surfaces reveals that the much stronger adsorption strength of 3-butenoic acid facilitates blocking of the interaction of surfaces with water molecules. Meanwhile, the calculated results indicate that adopting such an organic molecule as a passivation layer does not compromise their excellent electronic and optical properties. Our theoretical understanding of the A cation engineering and organic molecule-based surface passivation will be beneficial to the improvement of the overall performance of perovskite solar cells.

Metallic Cobalt-Carbon Composite as Recyclable and Robust Magnetic Photocatalyst for Efficient CO2 Reduction.

CO2 conversion into value-added chemical fuels driven by solar energy is an intriguing approach to address the current and future demand of energy supply. Currently, most reported surface-sensitized heterogeneous photocatalysts present poor activity and selectivity under visible light irradiation. Here, photosensitized porous metallic and magnetic 1200 CoC composites (PMMCoCC-1200) are coupled with a [Ru(bpy)3 ]Cl2 photosensitizer to efficiently reduce CO2 under visible-light irradiation in a selective and sustainable way. As a result, the CO production reaches a high yield of 1258.30 µL with selectivity of 64.21% in 6 h, superior to most reported heterogeneous photocatalysts. Systematic investigation demonstrates that the central metal cobalt is the active site for activating the adsorbed CO2 molecules and the surficial graphite carbon coating on cobalt metal is crucial for transferring the electrons from the triplet metal-to-ligand charge transfer of the photosensitizer Ru(bpy)32+ , which gives rise to significant enhancement for CO2 reduction efficiency. The fast electron injection from the excited Ru(bpy)32+ to PMMCoCC-1200 and the slow backward charge recombination result in a long-lived, charge-separated state for CO2 reduction. More impressively, the long-time stability and easy magnetic recycling ability of this metallic photocatalyst offer more benefits to the photocatalytic field.

Anomalies in the low frequency vibrational density of states for a polymer with intrinsic microporosity - the Boson peak of PIM-1.

Polymers with intrinsic microporosity are promising candidates for the active separation layer in gas separation membranes. Here, the vibrational density of states (VDOS) for PIM-1, the prototypical polymer with intrinsic microporosity, is investigated by means of inelastic neutron scattering. The results are compared to data measured for a more conventional high-performance polyimide used in gas separation membranes (Matrimid). The measured data show the characteristic low frequency excess contribution to VDOS above the Debye sound wave level, generally known as the Boson peak in glass-forming materials. In comparison to the Boson peak of Matrimid, that of PIM-1 is shifted to lower frequencies. This shift is discussed considering the microporous, sponge-like structure of PIM-1 as providing a higher compressibility at the molecular scale than for conventional polymers. For an annealed PIM-1 sample, the Boson peak shifts to higher frequencies in comparison to the un-annealed sample. These changes in the VDOS of the annealed PIM-1 sample are related to changes in the microporous structure as confirmed by X-ray scattering.

Ultrathin two-dimensional layered metal hydroxides: an emerging platform for advanced catalysis, energy conversion and storage.

The unique properties of graphene are triggering a great deal of attention toward the family of ultrathin two-dimensional (2D) structures. Ultrathin layered metal hydroxides (LMHs) are increasingly being recognized as an important category in 2D nanomaterials, and the corresponding research has been experiencing a significant renaissance. Due to the flexible tunability of metal ions, their naturally positively charged plane and 2D anisotropy with nanometre thickness, ultrathin LMHs and their derived hybrids have shown exciting perspectives in many fields, such as catalysis, and energy storage and conversion. As for practical application, ultrathin 2D LMHs have exhibited high performances in electrocatalysis (e.g. the hydrogen and oxygen evolution reactions), photocatalysis and supercapacitors. In particular, hybrid materials based on ultrathin LMHs have proven to further improve the catalytic performance by synergistic effects derived from the hybrid interfaces. Nevertheless, studies on ultrathin LMHs are still in the infant stage and lag far behind other important 2D nanomaterials. Hence, it is essential to update the reported work in this emerging research area. In this tutorial review, we aim to summarize recent developments in ultrathin LMHs and their derived hybrids. The quite dispersed literature regarding ultrathin LMH-based materials is classified under the framework of catalysis- and energy-related properties and applications.

Strongly Coupled CoCr2 O4 /Carbon Nanosheets as High Performance Electrocatalysts for Oxygen Evolution Reaction.

A strongly coupled CoCr2 O4 /carbon nanosheet composite is concurrently grown via a facile one-step molten-salt calcination approach. The strong coupling between carbon and CoCr2 O4 has improved the electrical conductivity and preserved the active sites in catalysts. These results may pave the way to improve the performance of spinel oxides as electrocatalysts for oxygen evolution reactions.

Calorimetric evidence for a mobile surface layer in ultrathin polymeric films: poly(2-vinyl pyridine).

Specific heat spectroscopy was used to study the dynamic glass transition of ultrathin poly(2-vinyl pyridine) films (thicknesses: 405-10 nm). The amplitude and the phase angle of the differential voltage were obtained as a measure of the complex heat capacity. In a traditional data analysis, the dynamic glass transition temperature Tg is estimated from the phase angle. These data showed no thickness dependency on Tg down to 22 nm (error of the measurement of ±3 K). A derivative-based method was established, evidencing a decrease in Tg with decreasing thickness up to 7 K, which can be explained by a surface layer. For ultrathin films, data showed broadening at the lower temperature side of the spectra, supporting the existence of a surface layer. Finally, temperature dependence of the heat capacity in the glassy and liquid states changes with film thickness, which can be considered as a confinement effect.

Enhanced photocatalytic hydrogen evolution through MoS2 quantum dots modification of bismuth-based perovskites.

Efficient and cost-effective photocatalysts are pivotal for advancing large-scale solar hydrogen generation. Herein, we report a composite photocatalyst by incorporating MoS2 quantum dots (MoS2 QDs) as a cocatalyst into Cs3Bi2I9, resulting in a high enhancement in photocatalytic performance. Remarkably, the optimum MoS2 QDs/Cs3Bi2I9 composite achieves an impressive hydrogen evolution rate (6.09 mmol h-1 g-1) in an ethanol and HI/H3PO2 mixed solution. This rate is 8.8 times higher than pristine Cs3Bi2I9 (0.69 mmol h-1 g-1) and notably surpasses Pt/Cs3Bi2I9 (2.47 mmol h-1 g-1). Moreover, the composite displays exceptional stability during an 18-hour reaction, showcasing its potential for sustainable photocatalytic hydrogen evolution.

Stabilization and Performance Enhancement Strategies for Halide Perovskite Photocatalysts.

Solar-energy-powered photocatalytic fuel production and chemical synthesis are widely recognized as viable technological solutions for a sustainable energy future. However, the requirement of high-performance photocatalysts is a major bottleneck. Halide perovskites, a category of diversified semiconductor materials with suitable energy-band-enabled high-light-utilization efficiencies, exceptionally long charge-carrier-diffusion-length-facilitated charge transport, and readily tailorable compositional, structural, and morphological properties, have emerged as a new class of photocatalysts for efficient hydrogen evolution, CO2 reduction, and various organic synthesis reactions. Despite the noticeable progress, the development of high-performance halide perovskite photocatalysts (HPPs) is still hindered by several key challenges: the strong ionic nature and high hydrolysis tendency induce instability and an unsatisfactory activity due to the need for a coactive component to realize redox processes. Herein, the recently developed advanced strategies to enhance the stability and photocatalytic activity of HPPs are comprehensively reviewed. The widely applicable stability enhancement strategies are first articulated, and the activity improvement strategies for fuel production and chemical synthesis are then explored. Finally, the challenges and future perspectives associated with the application of HPPs in efficient production of fuels and value-added chemicals are presented, indicating the irreplaceable role of the HPPs in the field of photocatalysis.

Oxygen-Coordinated Single Mn Sites for Efficient Electrocatalytic Nitrate Reduction to Ammonia.

Electrocatalytic nitrate reduction reaction has attracted increasing attention due to its goal of low carbon emission and environmental protection. Here, we report an efficient NitRR catalyst composed of single Mn sites with atomically dispersed oxygen (O) coordination on bacterial cellulose-converted graphitic carbon (Mn-O-C). Evidence of the atomically dispersed Mn-(O-C2)4 moieties embedding in the exposed basal plane of carbon surface is confirmed by X-ray absorption spectroscopy. As a result, the as-synthesized Mn-O-C catalyst exhibits superior NitRR activity with an NH3 yield rate (RNH3) of 1476.9 ± 62.6 µg h-1 cm-2 at - 0.7 V (vs. reversible hydrogen electrode, RHE) and a faradaic efficiency (FE) of 89.0 ± 3.8% at - 0.5 V (vs. RHE) under ambient conditions. Further, when evaluated with a practical flow cell, Mn-O-C shows a high RNH3 of 3706.7 ± 552.0 µg h-1 cm-2 at a current density of 100 mA cm-2, 2.5 times of that in the H cell. The in situ FT-IR and Raman spectroscopic studies combined with theoretical calculations indicate that the Mn-(O-C2)4 sites not only effectively inhibit the competitive hydrogen evolution reaction, but also greatly promote the adsorption and activation of nitrate (NO3-), thus boosting both the FE and selectivity of NH3 over Mn-(O-C2)4 sites.

Electrosynthesis of chlorine from seawater-like solution through single-atom catalysts.

The chlor-alkali process plays an essential and irreplaceable role in the modern chemical industry due to the wide-ranging applications of chlorine gas. However, the large overpotential and low selectivity of current chlorine evolution reaction (CER) electrocatalysts result in significant energy consumption during chlorine production. Herein, we report a highly active oxygen-coordinated ruthenium single-atom catalyst for the electrosynthesis of chlorine in seawater-like solutions. As a result, the as-prepared single-atom catalyst with Ru-O4 moiety (Ru-O4 SAM) exhibits an overpotential of only ~30 mV to achieve a current density of 10 mA cm-2 in an acidic medium (pH = 1) containing 1 M NaCl. Impressively, the flow cell equipped with Ru-O4 SAM electrode displays excellent stability and Cl2 selectivity over 1000 h continuous electrocatalysis at a high current density of 1000 mA cm-2. Operando characterizations and computational analysis reveal that compared with the benchmark RuO2 electrode, chloride ions preferentially adsorb directly onto the surface of Ru atoms on Ru-O4 SAM, thereby leading to a reduction in Gibbs free-energy barrier and an improvement in Cl2 selectivity during CER. This finding not only offers fundamental insights into the mechanisms of electrocatalysis but also provides a promising avenue for the electrochemical synthesis of chlorine from seawater electrocatalysis.

Operando Converting BiOCl into Bi2O2(CO3)xCly for Efficient Electrocatalytic Reduction of Carbon Dioxide to Formate.

Bismuth-based materials (e.g., metallic, oxides and subcarbonate) are emerged as promising electrocatalysts for converting CO2 to formate. However, Bio-based electrocatalysts possess high overpotentials, while bismuth oxides and subcarbonate encounter stability issues. This work is designated to exemplify that the operando synthesis can be an effective means to enhance the stability of electrocatalysts under operando CO2RR conditions. A synthetic approach is developed to electrochemically convert BiOCl into Cl-containing subcarbonate (Bi2O2(CO3)xCly) under operando CO2RR conditions. The systematic operando spectroscopic studies depict that BiOCl is converted to Bi2O2(CO3)xCly via a cathodic potential-promoted anion-exchange process. The operando synthesized Bi2O2(CO3)xCly can tolerate - 1.0 V versus RHE, while for the wet-chemistry synthesized pure Bi2O2CO3, the formation of metallic Bio occurs at - 0.6 V versus RHE. At - 0.8 V versus RHE, Bi2O2(CO3)xCly can readily attain a FEHCOO- of 97.9%, much higher than that of the pure Bi2O2CO3 (81.3%). DFT calculations indicate that differing from the pure Bi2O2CO3-catalyzed CO2RR, where formate is formed via a *OCHO intermediate step that requires a high energy input energy of 2.69 eV to proceed, the formation of HCOO- over Bi2O2(CO3)xCly has proceeded via a *COOH intermediate step that only requires low energy input of 2.56 eV.

Facile synthesis of high-concentration, stable aqueous dispersions of uniform silver nanoparticles using aniline as a reductant.

A facile method was developed for preparing uniform silver nanoparticles with small particle sizes of less than 10 nm at high concentrations, in which aniline was used to reduce silver nitrate (AgNO(3)) to silver nanoparticles in the presence of dodecylbenzenesulfonic acid (DBSA) as a stabilizer. Upon the addition of excess NaOH to the DBSA-aniline-AgNO(3) (DAA) system, the formation of silver nanoparticles was almost complete in just 2 min at 90 °C (in 94% yield). The average size of those resultant silver nanoparticles was 8.9 ± 1.1 nm, and the colloids were stable for more than 1 year at ambient temperature. A possible mechanism for the formation of silver nanoparticles was proposed to be related to two factors: one was the mesoscopic structures of the DAA system in which silver ions were restricted in the dispersed phases composed of DBSA and aniline; the other was Ag(2)O nanocrystallites generated in situ that could be readily reduced by aniline to small silver nanoparticles at high concentrations.

In Situ Growth of Ultrathin Ni(OH)2 Nanosheets as Catalyst for Electrocatalytic Oxidation Reactions.

Development of electrocatalysts that are capable of efficiently oxidizing biomass-derived 5-hydroxymethylfurfural (HMF) into 2,5-furandicarboxylic acid (FDCA) is critically important for production of degradable plastics via non-fossil routes. In this study, a facile and scalable immersion synthetic approach has been developed to grow ultrathin nickel hydroxide nanosheets in situ on commercial nickel foam (Ni(OH)2 /NF) as an anode for the electrocatalytic oxidation of HMF to FDCA with complete HMF conversion, 100 % FDCA yield, and >99 % faradaic efficiency at 1.39 V (vs. RHE) within 90 min. Mechanistic studies reveal that the initial oxidation of HMF takes place at the carbonyl group and FDCA is generated through two further oxidation steps. Impressively, the synthesized Ni(OH)2 /NF can also be used to electrocatalytically oxidize other alcohol/aldehyde-containing compounds to the targeted products in alkaline medium with 100 % yield and >94 % faradaic efficiency under a low oxidation potential of 1.39 V (vs. RHE) within short reaction times.

Rational design of metal oxide catalysts for electrocatalytic water splitting.

Electrocatalytic energy conversion between electricity and chemical bonding energy is realized through redox reactions with multiple charge transfer steps at the electrode-electrolyte interface. The surface atomic structure of the electrode materials, if appropriately designed, will provide an energetically affordable pathway with individual reaction intermediates that not only reduce the thermodynamic energy barrier but also allow an acceptably fast kinetic rate of the overall redox reaction. As one of the most abundant and stable forms, oxides of transitional metals demonstrated promising electrocatalytic activities towards multiple important chemical reactions. In this topical review, we attempt to discuss the possible avenues to construct the electrocatalytic active surface for this important class of materials for two essential chemical reactions for water splitting. A general introduction of the electrochemical water splitting process on the electrocatalyst surface with applied potential will be provided, followed by a discussion on the fundamental charge transfers and the mechanism. As the generally perceived active sites are chemical reaction dependent, we offer a general overview of the possible approaches to construct or create electrocatalytically active sites in the context of surface atomic structure engineering. The review concludes with perspectives that summarize challenges and opportunities in electrocatalysis and how these can be addressed to unlock the electrocatalytic potentials of the metal oxide materials.

2D Electrocatalysts for Converting Earth-Abundant Simple Molecules into Value-Added Commodity Chemicals: Recent Progress and Perspectives.

The electrocatalytic conversion of earth-abundant simple molecules into value-added commodity chemicals can transform current chemical production regimes with enormous socioeconomic and environmental benefits. For these applications, 2D electrocatalysts have emerged as a new class of high-performance electrocatalyst with massive forward-looking potential. Recent advances in 2D electrocatalysts are reviewed for emerging applications that utilize naturally existing H2 O, N2 , O2 , Cl- (seawater) and CH4 (natural gas) as reactants for nitrogen reduction (N2 → NH3 ), two-electron oxygen reduction (O2 → H2 O2 ), chlorine evolution (Cl- → Cl2 ), and methane partial oxidation (CH4 → CH3 OH) reactions to generate NH3 , H2 O2 , Cl2 , and CH3 OH. The unique 2D features and effective approaches that take advantage of such features to create high-performance 2D electrocatalysts are articulated with emphasis. To benefit the readers and expedite future progress, the challenges facing the future development of 2D electrocatalysts for each of the above reactions and the related perspectives are provided.

Phosphorus and Sulfur Co-Doped Cobaltous Oxide Synthesized by an Inorganic-Salt-Assisted Method: Reaction Mechanism and Electrocatalytic Application.

An inorganic-salt-assisted synthesis of non-metallic heteroatom (phosphorus and sulfur) co-doped cobaltous oxide (P/S-CoO) has been reported. Potassium sulphate (K2 SO4 ) was used as inorganic source of sulfur (S), while triphenyl phosphine (PPh3 ) was used as phosphorus (P) source. A stepwise mechanistic investigation into the doping process revealed that the decomposition of PPh3 triggered the release of both the elemental sulfur and phosphorus because of the reducing reaction environment. The transformation of cobalt-PPh3 complex into cubic cobalt (II) oxide along with the successful co-doping (P and S) was achieved by high temperature calcination at 800 °C but preserved the bulk CoO crystalline structure. The as synthesized P/S-CoO demonstrated an unprecedented enhancement on the oxygen evolution activity compare to that of pristine CoO with the current density of 10 mA/cm2 at the overpotential of 293 mV in 1.0 M KOH electrolyte and profound stability at different current densities.

Approaching the activity limit of CoSe2 for oxygen evolution via Fe doping and Co vacancy.

Electronic structure engineering lies at the heart of efficient catalyst design. Most previous studies, however, utilize only one technique to modulate the electronic structure, and therefore optimal electronic states are hard to be achieved. In this work, we incorporate both Fe dopants and Co vacancies into atomically thin CoSe2 nanobelts for /coxygen evolution catalysis, and the resulted CoSe2-DFe-VCo exhibits much higher catalytic activity than other defect-activated CoSe2 and previously reported FeCo compounds. Deep characterizations and theoretical calculations identify the most active center of Co2 site that is adjacent to the VCo-nearest surface Fe site. Fe doping and Co vacancy synergistically tune the electronic states of Co2 to a near-optimal value, resulting in greatly decreased binding energy of OH* (ΔEOH) without changing ΔEO, and consequently lowering the catalytic overpotential. The proper combination of multiple defect structures is promising to unlock the catalytic power of different catalysts for various electrochemical reactions.

Coexisting Single-Atomic Fe and Ni Sites on Hierarchically Ordered Porous Carbon as a Highly Efficient ORR Electrocatalyst.

The development of oxygen reduction reaction (ORR) electrocatalysts based on earth-abundant nonprecious materials is critically important for sustainable large-scale applications of fuel cells and metal-air batteries. Herein, a hetero-single-atom (h-SA) ORR electrocatalyst is presented, which has atomically dispersed Fe and Ni coanchored to a microsized nitrogen-doped graphitic carbon support with unique trimodal-porous structure configured by highly ordered macropores interconnected through mesopores. Extended X-ray absorption fine structure spectra confirm that Fe- and Ni-SAs are affixed to the carbon support via FeN4 and NiN4 coordination bonds. The resultant Fe/Ni h-SA electrocatalyst exhibits an outstanding ORR activity, outperforming SA electrocatalysts with only Fe- or Ni-SAs, and the benchmark Pt/C. The obtained experimental results indicate that the achieved outstanding ORR performance results from the synergetic enhancement induced by the coexisting FeN4 and NiN4 sites, and the superior mass-transfer capability promoted by the trimodal-porous-structured carbon support.