X-ray Adsorption Research Articles

Efficient selective hydrogenation of phenylacetylene over Pd-based rare earth dual-atomic catalysts

Selective hydrogenation of phenylacetylene to styrene plays a vital role in fine chemical synthesis with palladium (Pd)-based catalysts as the active components and usually suffered from low selectivity due to over-hydrogenation and low stability through polymerization (c.a. green oil generation). In this work, we found that by confining the Pd atom within a Pd-Ln (Ln: rare earth elements, such as Y, Lu, etc. ) diatomic structure [diatomic catalyst (DAC)], the reaction performance of selective hydrogenation of phenylacetylene has been greatly promoted, in which 92% styrene selectivity has been determined at 100% phenylacetylene conversion. This would be attributed to the diatomic structure established, which was achieved by introducing Pd-Ln precursors and confirmed by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and X-ray adsorption fine structure (XAFS) characterizations and it was demonstrated that slight electron transfer from Ln to the adjacent isolated Pd makes it slightly negatively charged and facilitated the styrene formation. Besides, a Langmuir-Hinshelwood model was established to describe the whole reaction mechanism. After a systematic kinetic investigation, it suggests that the C8H6* + H* elementary step is probably the kinetically relevant for the whole reaction and the surface of the catalyst is mainly covered by C8H6*. The energy relationship of each step along phenylacetylene hydrogenation was quantitatively described by means of parity fitting and gas isothermal adsorption, providing insights into the selective hydrogenation of phenylacetylene over 0.02%Pd-Ln/C (Ln = Y/Lu) catalysts and pave the way of catalytic design at the atomic level.

Solanum tuberosum leaf extract as an eco-friendly corrosion inhibitor for Q235-steel in HCl medium: Experimental and theoretical evaluation

Solanum tuberosum leaf extract (STLs), used as a biodegradable corrosion inhibitor, was prepared to mitigate the corrosion rate of Q235 steel in HCl medium. The active inhibitory components existing in STLs were tracked by Fourier transform infrared spectroscopy. Electrochemical measurements, morphological characterization and contact angle tests were combined to evaluate the anti-corrosion performance of STLs at various concentrations and different temperatures, and the results show that the addition of STLs can evidently magnify the charge transfer resistance, expand the double layer capacitance at electric/solution interface, and simultaneously reduce the corrosion current density of Q235 steel in HCl medium with the maximum inhibition efficiency of 91.89 %. The adsorption behavior of STLs on steel was investigated using X-ray photoelectron spectroscopy and adsorption models. It is revealed that the molecules of STLs spontaneously bind to the substrate through chemical and physical action, forming a protective layer to block the diffusion pathway of harsh ions. Furthermore, theoretical calculations confirm that Solanum tuberosum leaves components were adsorbed on steel substrates through donor-acceptor interactions.

Synchrotron-aided exploration of REE recovery from coal fly ashes within a Canadian context

Coal ashes in Canada have gained attention as a potential source for recovering rare earth elements (REE) from industrial waste. However, the complex chemical properties of coal ashes have made it difficult to determine the desirability, feasibility, and viability of REE recovery. To address this issue, this study systematically investigated distribution and structural information, speciation and chemical-binding state, and purity and extraction capacity of REE in multiple Canadian coal ashes (i.e., 2 fly ash and 1 bottom ash samples) through synchrotron-based X-ray fluorescence mapping and adsorption spectrum analyses, as well as high-resolution REE sequential extraction quantitation. The results showed that Y, Ce, and La were present in the glass phase of the bottom ash, and the distributions of these REE elements correlated with Ca. The XANES analysis revealed that the dominant form of REE in coal fly ash (CFA) was REE oxides, indicating a transformation during combustion, while Y2O3 and Y2(CO3)3 were the predominant Y species identified in CFA. The study found that there is no correlation between P and REEs, suggesting that REEs in CFA may exist as discrete particles rather than being associated with amorphous glass. The extractability of REEs in bottom ash samples was lower than that in fly ash samples. Additionally, the benefits of REE recovery were estimated to be USD 99.82 to 215.21 per ton of fly ash through life cycle analysis, indicating that REE recovery from fly ashes is a promising path to supplement the REE supply chain in Canada.

Bimetal-organic framework derived single-atom-like Co/Fe catalysts for peroxydisulfate activation: The dual amplification of radical and nonradical pathways

A novel single-atom-like Co/Fe catalyst (i.e., Co/Fe-N-C) was synthesized by pyrolysis of a Zn/Co/Fe zeolitic imidazolate framework, and applied in peroxydisulfate (PDS) activation for removal of organic contaminants from wastewater. The isolated diatomic metal-nitrogen sites were detected by X-ray adsorption fine-structure. The degradation of four contaminants (i.e., phenol, bisphenol A, 2,4-dichlorophenol, and N-methyl-2-pyrrolidone) with a concentration of 100 mg/L could be degraded separately within 20 min by the Co/Fe-N-C system with 10 mmol/L of PDS, 0.5 g/L of catalyst dosage, and initial pH of 3. Besides, 79.2 % of phenol could be mineralized in 120 min, and the turn-over frequency value of the catalyst was calculated to be 27.17 min−1, which was higher than the commonly reported homogeneous PS-AOPs. Moreover, the Co/Fe-N-C exhibited high stability (mineralization rate over 70 % after 5 cycles), a wide initial pH range (3−9), and high catalytic performance at 5–20 mmol/L of PDS concentrations. Based on the analysis of radical scavenging experiments and electron spin resonance spectra, the radical and non-radical pathways for PDS activation were proved in the system, and the contribution of phenol degradation by each pathway was clarified.

Bonding and Interactions in UO22+ for Ground and Core Excited States: Extracting Chemistry from Molecular Orbital Calculations.

Theoretical analyses of actinyls are necessary in order to understand and correctly interpret the chemical and physical properties of these molecules. Here, wave functions of Uranyl, UO22+, are considered for the ground state and for the core excited states where an electron is promoted from the U 3d5/2 shell into a low-lying unoccupied orbital that is U 5f antibonding with the ligand, O, orbitals. A focus is on the application of novel theoretical methods to the analysis of these wave functions so that measurements, especially with X-ray absorption, can be related to the UO22+ chemical bonding. The bond covalency is examined with these theoretical methods. The study includes how the covalent character is different for the ground and excited configurations and how this character changes as the U-O distance is changed. Furthermore, analyses are mode of how many-body effects may modify excitation energies and X-ray adsorption intensities. This includes determining the extent to which a single configuration provides a satisfactory model for the UO22+ wave functions. Two distinct types of many-body effects are considered. One involves the angular momentum coupling of the open shell electrons in the excited states to yield correct multiplets. The second adds excitations from shells that are bonding into the antibonding open shell space. These excitations are essential to properly describe the X-ray adsorption. While these many-body effects must be taken into account, their importance and their role can be explained and understood using orbitals and orbital occupations.

Synergistic effect of Ru single atoms and MnO2 to boost oxygen reduction/evolution activity via strong electronic interaction

Ru-based single-atomic catalysts have shown great potential application in sustainable electrochemical energy conversion/storage devices. Herein Ru single atoms anchored on the surface of MnO2 nanorods (Ru SAs@MnO2) have been successfully constructed by a facile low-temperature solid-phase reaction, which has been confirmed by X-ray adsorption spectra. The synthesized Ru SAs@MnO2 catalyst exhibits a comparable ORR performance with half-wave potential of 0.83 V and a limiting current density of 7.1 mA cm−2 to commercial Pt/C, and high OER performance with the overpotential of 320 mV at 10 mA cm−2. Theoretical calculation results indicate that Mn sites and Ru sites of Ru SAs@MnO2 act as the catalytic ORR and OER sites, respectively, and the synergistic effect between Ru SAs and MnO2 contributes to the improved catalytic performance via strong electronic interaction. When assembled zinc-air batteries, a maximum power density 230.0 mW cm−2 could be delivered at 318.5 mA cm−2.

Kinetics-Driven Crystal Facet Evolution Mechanism of Atomically Ordered Intermetallic PtFe Nanocubes toward Electrochemical Catalysis.

Crystal structure engineering in nanoparticles has been regarded as a vital method in catalyst development and design. Herein, PtFe nanocubes, manufactured with ordered PtFe intermetallic structure and a desired facet of {202}, have been successfully prepared via the combination of selective deposition strategy and spatial barrier effect. In-situ X-ray photoelectron spectroscopy found that the growth of the high-index facet and formation of the nanocube for o-PtFe-202 materials arise from the surface Fe2+ modification stabilized effect and the selective deposition of Cl-, respectively. Moreover, density functional theory calculations and X-ray adsorption spectroscopies further proved that the improved oxygen reduction reaction activity and stability of o-PtFe-202 mainly originate from the synergistic effect of the desired high-index facet, ordered crystal structure, and resulting optimal d-band center of Pt. As expected, the o-PtFe-202 exhibits excellent mass activity (2.48 mA·ugPt-1) and specific activity (7.78 mA·cm-2), with only a 7.3% decrease in mass activity after 30 000 cycles.

Oxygen Functional Groups Regulate Cobalt-Porphyrin Molecular Electrocatalyst for Acidic H2O2 Electrosynthesis at Industrial-Level Current.

Electrosynthesis of hydrogen peroxide (H2O2) based on proton exchange membrane (PEM) reactor represents a promising approach to industrial-level H2O2 production, while it is hampered by the lack of high-efficiency electrocatalysts in acidic medium. Herein, we present a strategy for the specific oxygen functional group (OFG) regulation to promote the H2O2 selectivity up to 92 % in acid on cobalt-porphyrin molecular assembled with reduced graphene oxide. In situ X-ray adsorption spectroscopy, in situ Raman spectroscopy and Kelvin probe force microscopy combined with theoretical calculation unravel that different OFGs exert distinctive regulation effects on the electronic structure of Co center through either remote (carboxyl and epoxy) or vicinal (hydroxyl) interaction manners, thus leading to the opposite influences on the promotion in 2e- ORR selectivity. As a consequence, the PEM electrolyzer integrated with the optimized catalyst can continuously and stably produce the high-concentration of ca. 7 wt % pure H2O2 aqueous solution at 400 mA cm-2 over 200 h with a cell voltage as low as ca. 2.1 V, suggesting the application potential in industrial-scale H2O2 electrosynthesis.

The critical role of organic matter for cadmium-lead interactions in soil: Mechanisms and risks

Understanding the interaction mechanisms between complex heavy metals and soil components is a prerequisite for effectively forecasting the mobility and availability of contaminants in soils. Soil organic matter (SOM), with its diverse functional groups, has long been a focal point of research interest. In this study, four soils with manipulated levels of SOM, cadmium (Cd) and lead (Pb) were subjected to a 90-day incubation experiment. The competitive interactions between Cd and Pb in soils were investigated using Fourier transform infrared spectrometer (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and X-ray adsorption near-edge structure (XANES) analysis. Our results indicate that Pb competed with Cd for adsorption sites on the surface of SOM, particularly on carboxyl and hydroxyl functional groups. Approximately 22.6 % of Cd adsorption sites on humus were occupied by Pb. The use of sequentially extracted exchangeable heavy metals as indicators for environment risk assessments, considering variations in soil physico-chemical properties and synergistic or antagonistic effects between contaminants, provides a better estimation of metal bioavailability and its potential impacts. Integrating comprehensive contamination characterization of heavy metal interactions with the soil organic phase is an important advancement to assess the environmental risks of heavy metal dynamics in soil compared to individual contamination assessments.

Rubik’s cube PBA frameworks for optimizing the electrochemical performance in alkali metal-ion batteries

PBA frameworks have stood out among metal–organic frameworks because of their easy preparation, excellent stability, porous structures, and rich redox properties. Unfortunately, their non-ideal conductivity and significant volume expansion during cycling prevent more widespread application in alkali-metal-ion (Li+, Na+, and K+) batteries. By changing the type and molar ratio of metal ions, Rubik’s PBA frameworks with infinite structural variations were obtained in this study, just like the Rubik’s cube undergoes infinite changes during the rotation. X-ray adsorption fine structure measurements have documented the existence and determined the coordination environment of the metal ions in the Rubik’s PBA framework. Benefiting from the more stable Rubik’s cube structures with diverse composition, enhanced conductivity, and greater adsorption capacity, the obtained Rubik’s cubes CoM-PBA anodes, especially CoZn-PBA deliver the enhanced cycling and rate performance in all the alkali-metal-ion batteries. The findings are supported by density functional theory calculations. Ex-situ X-ray photoelectron spectroscopy, and in-situ X-ray diffraction measurements were undertaken to explore the storage mechanism of CoZn-PBA anodes. Our results further demonstrate that the Rubik’s cube PBA framework-based materials could be widely applied in the field of alkali-metal-ion batteries.

Surface pretreatment of scheelite and cassiterite by gallic acid to achieve high efficiency flotation separation

Scheelite and cassiterite are common tungsten and tin oxide minerals that often coexist in nature. However, the similar oxidation degrees and solution and surface chemical properties of scheelite and cassiterite pose challenges to their flotation separation. Moreover, research in this area is currently limited. This study investigated the selective depression mechanism of gallic acid (GA) in the flotation separation of scheelite and cassiterite and successfully achieved the effective separation of the two minerals. Single mineral and artificially mixed mineral experiments were performed to analyze the flotation separation behavior of scheelite and cassiterite. The results revealed that in the absence of a depressant, scheelite and cassiterite exhibited recovery of 93.43 % and 89.72 %, respectively. After the addition of 5 × 10−4 mol/L GA to the mineral slurry, the grades of WO3 and Sn in the flotation concentrates were 48.93 % and 18.13 %, with recovery of 82.50 % and 31.62 %, respectively. Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, zeta potential, adsorption amount, contact angle, and atomic force microscopy imaging analyses were conducted to examine the selective depression mechanism of GA in the flotation separation of scheelite and cassiterite. In the slurry, the cassiterite surface provided active Sn sites for the chemical adsorption of GA. Moreover, the phenolate O- donor atoms of the deprotonated polar groups of GA will undergo coordination with metal ions and then adsorb on the mineral surface. GA forms metal gallate through adsorption of its –COOH and –OH groups on mineral surface and produces textured oxide layer rich in OH groups, thus reducing the surface hydrophobicity of cassiterite and then depressing cassiterite. The selective adsorption of GA on the cassiterite surface hindered the further adsorption of NaOL, thereby reducing its surface hydrophobicity. Therefore, GA finally realized the flotation separation of the two minerals.

A novel Cu-doped ZnO confined structure: Precisely preparation, and sensitization mechanism for ppb-level H2S gas detection

It is still highly desired and challengeable to design H2S sensor with high selectivity and sensitivity due to its toxicity and new application in biomarkers like monitoring halitosis. Here, we reported a novel confined structure as highly sensitive and selective H2S gas sensor. The sensing material was prepared with a HKUST-1 templated method by atomic layer deposition (ALD) ZnO decorated on HKUST-1 and calcination. The gas sensor exhibits a high gas sensitivity (Ra/Rg = 2.67 @ 2 ppm) with excellent selectivity to H2S. Furthermore, the obtained sensor shows ppb-level detection ability (Ra/Rg = 1.13 @ 0.1 ppm). Apart from releasing electrons by the oxidization of H2S on oxygen vacancies with adsorbed oxygen species O2− on ZnO surface (Langmuir-Hinshelwood mechanism), the Cu was proved to be the active sites, and would react with surficial S species. The suggestion was confirmed by operando XAS (X-ray adsorption spectrum) measurements combined with DFT calculations (Mars-van Krevelen mechanism). This work provides valuable insights for developing efficient sensing materials and understanding the sensing mechanism.

Suppressing Metal Leaching and Sintering in Hydroformylation Reaction by Modulating the Coordination of Rh Single Atoms with Reactants.

Hydroformylation reaction is one of the largest homogeneously catalyzed industrial processes yet suffers from difficulty and high cost in catalyst separation and recovery. Heterogeneous single-atom catalysts (SACs), on the other hand, have emerged as a promising alternative due to their high initial activity and reasonable regioselectivity. Nevertheless, the stability of SACs against metal aggregation and leaching during the reaction has rarely been addressed. Herein, we elucidate the mechanism of Rh aggregation and leaching by investigating the structural evolution of Rh1@silicalite-1 SAC in response to different adsorbates (CO, H2, alkene, and aldehydes) by using diffuse reflectance infrared Fourier transform spectroscopy, X-ray adsorption fine structure, and scanning transmission electron microscopy techniques and kinetic studies. It is discovered that the aggregation and leaching of Rh are induced by the strong adsorption of CO and aldehydes on Rh, as well as the reduction of Rh3+ by CO/H2 which weakens the binding of Rh with support. In contrast, alkene effectively counteracts this effect by the competitive adsorption on Rh atoms with CO/aldehyde, and the disintegration of Rh clusters. Based on these results, we propose a strategy to conduct the reaction under conditions of high alkene concentration, which proves to be able to stabilize Rh single atom against aggregation and/or leaching for more than 100 h time-on-stream.

Precise modulation of surface lattice to reinforce structural stability of high-nickel layered oxide cathode by hafnium gradient doping

The quest for high-energy lithium-ion batteries has intensified interest in high-nickel layered oxide cathode materials, while the rise in nickel content adversely impacts structural stability and cycling performance. Herein, Hafnium (Hf) anchored at nickel (Ni) site precisely modulates the surface crystal lattice of high-nickel cathode (LiNi0.9Co0.05Mn0.05O2, NCM90) that is confirmed by Rietveld refinement of neutron powder diffraction. Notably, the strengthened structural stability thanks to Hf gradient doping is firmly substantiated by in-situ X-ray diffraction and in-situ X-ray adsorption spectroscopy. This enhancement can be ascribed to the substantial atomic mass of Hf and large radius of Hf4+, facilitating the minimization of potential alterations of interlayer or intralayer. The intensified Hf-O bond significantly increases the formation energy of oxygen vacancies and efficiently restrains the detrimental Li+/Ni2+ disorder, thereby mitigating lattice oxygen loss and enhancing both cycling and thermal stability of high-nickel cathode. Consequently, the 0.3 % Hf-doping cathode exhibits considerable improvement in electrochemical performance, delivering superior capacity retention of 95.0% after 100 cycles at 1C (1 C = 200 mA g−1) and 83.9 % after 500 cycles at 1C/5C in the voltage range of 3.0∼4.3 V. This work highlights the benefits of precise modulation strategy for high-nickel cathodes, offering a viable approach to enhance structural stability and electrochemical performance of high-nickel cathodes.

Oxygen-Bridged Cu Binuclear Sites for Efficient Electrocatalytic CO2 Reduction to Ethanol at Ultralow Overpotential.

Electrocatalytic CO2 reduction (CO2RR) to alcohols offers a promising strategy for converting waste CO2 into valuable fuels/chemicals but usually requires large overpotentials. Herein, we report a catalyst comprising unique oxygen-bridged Cu binuclear sites (CuOCu-N4) with a Cu···Cu distance of 3.0-3.1 Å and concomitant conventional Cu-N4 mononuclear sites on hierarchical nitrogen-doped carbon nanocages (hNCNCs). The catalyst exhibits a state-of-the-art low overpotential of 0.19 V (versus reversible hydrogen electrode) for ethanol and an outstanding ethanol Faradaic efficiency of 56.3% at an ultralow potential of -0.30 V, with high-stable Cu active-site structures during the CO2RR as confirmed by operando X-ray adsorption fine structure characterization. Theoretical simulations reveal that CuOCu-N4 binuclear sites greatly enhance the C-C coupling at low potentials, while Cu-N4 mononuclear sites and the hNCNC support increase the local CO concentration and ethanol production on CuOCu-N4. This study provides a convenient approach to advanced Cu binuclear site catalysts for CO2RR to ethanol with a deep understanding of the mechanism.

Developing high-power Li||S batteries via transition metal/carbon nanocomposite electrocatalyst engineering.

The activity of electrocatalysts for the sulfur reduction reaction (SRR) can be represented using volcano plots, which describe specific thermodynamic trends. However, a kinetic trend that describes the SRR at high current rates is not yet available, limiting our understanding of kinetics variations and hindering the development of high-power Li||S batteries. Here, using Le Chatelier's principle as a guideline, we establish an SRR kinetic trend that correlates polysulfide concentrations with kinetic currents. Synchrotron X-ray adsorption spectroscopy measurements and molecular orbital computations reveal the role of orbital occupancy in transition metal-based catalysts in determining polysulfide concentrations and thus SRR kinetic predictions. Using the kinetic trend, we design a nanocomposite electrocatalyst that comprises a carbon material and CoZn clusters. When the electrocatalyst is used in a sulfur-based positive electrode (5 mg cm-2 of S loading), the corresponding Li||S coin cell (with an electrolyte:S mass ratio of 4.8) can be cycled for 1,000 cycles at 8 C (that is, 13.4 A gS-1, based on the mass of sulfur) and 25 °C. This cell demonstrates a discharge capacity retention of about 75% (final discharge capacity of 500 mAh gS-1) corresponding to an initial specific power of 26,120 W kgS-1 and specific energy of 1,306 Wh kgS-1.

Effect of Ca Modified Biochar on the Chemical Speciation of Soil Phosphorus and Its Stabilization Mechanism

To control of phosphorus release from soil after farmland inundation around the lake and reservoir， calcium modified biochar （Ca-BC） was prepared using the coprecipitation method. Through X-ray photoelectron spectroscopy （XPS）， X-ray polycrystalline powder diffraction （XRD）， adsorption experiments， and simulated culture experiments， the effects of Ca-based biochar on the fraction of soil phosphorus （P） and its stabilization mechanism were studied. The results showed that the adsorption process of Ca-based modified biochar conformed to Langmuir （R2 = 0.940） and the first-order adsorption kinetic model （R2 = 0.961）， indicating that the P adsorption was a single-layer adsorption dominated by chemical action， and the maximum adsorption capacity was 267.93 mg·g-1. The simulated culture experiment indicated that when the modified biochar was 1%， the exchangeable fraction of phosphorus in the soil decreased from 7.42% to 4.59%. The XRD results demonstrated that Ca3（PO4）2 and hydroxyapatite absorption peaks appeared after adsorbed phosphorus on biochar， which proved that phosphate formed a relatively stable crystal precipitation. As shown in the XPS spectrum analysis， the carbonyl functional groups participated in the phosphorus fixation process， which improved the adsorption capacity of biochar for phosphorus. In general， when the concentration of Ca-based modified biochar was greater than 1%， it had a good fixation capacity for phosphorus release and had potential application value for controlling phosphorus release in soil.

Effective Strategy toward Obtaining Reliable Breakthrough Curves of Solid Adsorbents.

Metal-organic frameworks (MOFs) have demonstrated their versatility in a wide range of applications, including chemical separation, gas capture, and storage. In industrial adsorption processes, MOFs are integral to the creation of selective gas adsorption fixed beds. In this context, the assessment of their separation performance under relevant conditions often relies on breakthrough experiments. One aspect frequently overlooked in these experiments is the shaping of MOF powders, which can significantly impact the accuracy of breakthrough results. In this study, we present an approach for immobilizing MOF particles on the surface of glass beads (GBs) utilizing trimethylolpropane triglycidyl ether (TMPTGE) as a binder, leading to the creation of MOF@GB materials. We successfully synthesized five targeted MOF composites, namely, SIFSIX-3-Ni@GB, CALF-20@GB, UiO-66@GB, HKUST-1@GB, and MOF-808@GB, each possessing distinct pore sizes and structural topologies. Characterization studies employing powder X-ray diffraction and adsorption isotherm analyses demonstrated that MOFs@GB retained their crystallinity and 73-90% of the Brunauer-Emmett-Teller area of their parent MOFs. Dynamic breakthrough experiments revealed that, in comparison to their parent MOFs, MOF@GB configurations enhanced the accuracy of breakthrough measurements by mitigating pressure buildup and minimizing reductions in the gas flow rate. This work underscores the significance of meticulous experimental design, specifically in shaping MOF powders, to optimize the efficacy of breakthrough experiments. Our proposed strategy aims to provide a versatile platform for MOF powder processing, thereby facilitating more reliable breakthrough experiments.

Ru Single Atoms Integrated into Cobalt Oxide Spinel Structure with Interstitial Carbon for Enhanced Electrocatalytic Water Oxidation.

Oxygen evolution reaction (OER) plays a critical role in energy conversion technologies. Significant progress has been made in alkaline conditions. In contrast, it remains a challenge to develop stable OER electrocatalysts in acidic conditions. Herein, a new strategy is reported to stabilize single atoms integrated into cobalt oxide spinel structure with interstitial carbon (Ru0.27Co2.73O4), where the optimized Ru0.27Co2.73O4 exhibits a low overpotential of 265, 326, and 367mV to reach a current density of 10, 50, and 100mA cm2, respectively. More importantly, Ru0.27Co2.73O4 has long-term stability of up to 100h, representing one of the most stable OER electrocatalysts. X-ray adsorption spectroscopy (XAS) characterization and density functional theory (DFT) calculations jointly demonstrate that the significant catalytic performance of Ru0.27Co2.73O4 is due to the synergistic effect between the Ru and Co sites and the bridging O ligands, as well as the significant reduction of the OER energy barrier. This work provides a new perspective for designing and constructing efficient non-noble metal-based electrocatalysts for water splitting.

Revealing proton-coupled exchange mechanism in aqueous ion-exchange synthesis of nickel-rich layered cathodes for lithium-ion batteries

Ion exchange is a promising synthetic method for alleviating severe cation mixing in traditional layered oxide materials for lithium-ion batteries, leading to enhanced structural stability. However, the underlying mechanisms of ion exchange are still not fully understood. Such a fundamental study of the ion-exchange mechanism is needed for achieving the controllable synthesis of layered oxides with a stable structure. Herein, we thoroughly unearth the underlying mechanism that triggers the ion exchange of Ni-rich materials in aqueous solutions by examining time-resolved structural evolution combined with theoretical calculations. Our results reveal that the reaction pathway of ion exchange can be divided into two steps: protonation and lithiation. The proton is the key to achieving charge balance in the ion exchange process, as revealed by X-ray adsorption spectroscopy and inductive coupled plasma analysis. In addition, the intermediate product shows high lattice distortion during ion exchange, but it ends up with a most stable product with high lattice energy. Such apparent discrepancies in lattice energy between materials before and after ion exchange emphasize the importance of synthetic design in structural stability. This work provides new insights into the ion-exchange synthesis of Ni-rich oxide materials, which advances the development of cathode materials for high-performance lithium-ion batteries.