Average Valence State Research Articles

Unusually improved peracetic acid activation for ultrafast organic compound removal through redox-inert Mg incorporation into active Co3O4

Peracetic acid (PAA) is increasingly used in advanced oxidation processes (AOPs) for water purification, yet there remains a critical need for highly-efficient and low-cost activators. Here, we constructed abundant oxygen vacancies (OVs) into redox-active Co3O4 by incorporating redox-inert Mg species (MgCoOx), achieving ultrafast degradation of sulfamethoxazole (SMX) via PAA activation. The MgCoOx/PAA system successfully degraded SMX within 3 min, with a removal rate 154.8 times higher than the Co3O4/PAA system, surpassing even previously reported single-atom catalysts. The primary active species identified was the acetylperoxyl radical (CH3C(O)OO•), with CoIV-oxo acting as a secondary active species that produced 18O-labeled sulfone compounds. We proposed a novel mechanism involving redox-inert Mg species that simultaneously strengthened PAA adsorption and activation. The enriched surface hydroxyl groups after Mg incorporation elevated the affinity for PAA binding. Meanwhile, the reduced Co average valence state and enhanced electron transfer capability facilitated PAA activation. This study offers an in-depth knowledge of redox-inert alkaline earth metals in PAA-AOPs.

The enhancement and impact of Se doping on the electrochemical properties of LiMn2O4 cathode material for aqueous Li-ion batteries

Spinel LiMn2O4 is a promising cathode material for lithium-ion batteries. However, due to the Jahn-Teller effect and Mn dissolution, its capacity decreases seriously in the cycle process, which hinders its wider application. In the course of our research, we discovered that a modest infusion of Se-doping is capable of significantly augmenting the oxygen vacancy within the material, improve the conductivity of the LiMn2O4 material and promotes superior battery performance. Moreover, due to Se-doped the average valence state of Mn is raised, which effectively mitigates the Jahn-Teller effect. The optimized sample exhibits high capacity, long cycle life, and superior rate capability, with an initial discharge specific capacity of 101.0 mAh·g−1 at 7 C and capacity retention of 87.3 % after 200 cycles. The maximum specific discharge capacity of the full battery during the cycle was 97.9 mAh·g−1, the capacity retention rate after 200 cycles was 78.2 %, and the maximum energy density during the cycle is 145.1 Wh·Kg−1, which was nearly twice that of the single lithium-ion battery in this paper. The effect of Se-doped on the properties of LiMn2O4 cathode materials provides a new idea for the development of high-performance spinel lithium manganese oxide cathode materials.

Performance improvement of oxygen electrode in reversible protonic ceramic electrochemical cell by co-doping of La and F

Reversible protonic ceramic electrochemical cell (R-PCEC) has demonstrated high potential as an energy storage and conversion device. Efforts have primarily concentrated on the development of oxygen electrodes being to increase their performance and reduce performance degradation. In this work, three perovskite materials, namely Ba0.9Co0.2Fe0.7Nb0.1O3-δ (BCFN), Ba0.8La0.1Co0.2Fe0.7Nb0.1O3-δ (BLCFN), and Ba0.8La0.1Co0.2Fe0.7Nb0.1F0.1O2.9-δ (BLCFNF) are investigated. Both doping with La and co-doping with La and F lead to a notable reduction in the average valence states of Fe, Co, and Nb elements, further resulting in an increase in oxygen vacancy concentration, thereby enhancing the oxygen migration ability of the material. The H2O partial pressure does not have a significant impact on the polarization resistance (Rp) of the oxygen electrode. Conversely, the rise in Rp is highly correlated with the decrease in oxygen partial pressure, suggesting that the primary factor influencing the reaction rate of the oxygen electrode process is the exchange of oxygen ions on the surface of the electrode. BLCFNF exhibits the best oxygen migration and surface exchange ability, resulting in the lowest Rp. When BLCFNF was used as the oxygen electrode in a R-PCEC with the humidity air (10%H2O) and humidified H2 (3%H2O) as oxidant and fuel, respectively, it exhibits the highest maximum power density of 472 mW cm−2, and a current density of −682.6 mA cm−2 (1.3 V) at 650 °C. In addition, BLCFNF also shows good durability in both discharge and electrolysis process. The results indicate that La and F co-doped BLCFNF material is a promising oxygen electrode material for R-PCECs.

Dynamic (Sub)surface-Oxygen Enables Highly Efficient Carbonyl-Coupling for Electrochemical Carbon Dioxide Reduction.

Nowadays, high-valent Cu species (i.e., Cuδ +) are clarified to enhance multi-carbon production in electrochemical CO2 reduction reaction (CO2RR). Nonetheless, the inconsistent average Cu valence states are reported to significantly govern the product profile of CO2RR, which may lead to misunderstanding of the enhanced mechanism for multi-carbon production and results in ambiguous roles of high-valent Cu species. Dynamic Cuδ + during CO2RR leads to erratic valence states and challenges of high-valent species determination. Herein, an alternative descriptor of (sub)surface oxygen, the (sub)surface-oxygenated degree (κ), is proposed to quantify the active high-valent Cu species on the (sub)surface, which regulates the multi-carbon production of CO2RR. The κ validates a strong correlation to the carbonyl (*CO) coupling efficiency and is the critical factor for the multi-carbon enhancement, in which an optimized Cu2O@Pd2.31 achieves the multi-carbon partial current density of ≈330 mA cm-2 with a faradaic efficiency of 83.5%. This work shows a promising way to unveil the role of high-valent species and further achieve carbon neutralization.

Sr-substitution effects on crystal structure and thermoelectric properties of misfit layered cobaltate, [Ca2CoO3]pCoO2

Misfit-layered cobaltate [Ca2CoO3]pCoO2 is a promising thermoelectric (TE) material that can operate at high temperature in air. Partial substitution of Ca with Sr has been suggested to enhance TE properties. To comprehend the unresolved effects of Sr-substitution on the TE properties, we have prepared single-phase polycrystalline samples of Sr-substituted [Ca2CoO3]pCoO2, i.e., [(Ca1-xSrx)2CoO3]pCoO2, using a spark plasma sintering (SPS) method followed by O2 annealing. We analyzed the crystal structure by powder X-ray diffraction, evaluated the average valence state of Co ions by X-ray photoelectron spectroscopy, and measured temperature-dependent TE properties. Upon Sr-substitution, the average valence state of Co ions slightly increased. The electrical resistivity perpendicular to the SPS pressing direction increased, while that along the SPS pressing direction was almost unchanged. The Seebeck coefficient and the thermal conductivity were less affected by the Sr-substitution. The figure-of-merit zT perpendicular to the SPS pressing direction tended to decrease with Sr-substitution, reflecting the increase in electrical resistivity.

Decoupling the Synergy Between PGM and PGM-Free Moieties toward Oxygen Reduction Reaction.

Recently, coupling the conventional low Pt-group-metal (low-PGM, LP) and emerging PGM-free (PF) moiety to form a composite LP/PF catalyst is proposed to be an advanced strategy to improve the intrinsic activity and stability of oxygen reduction reaction (ORR) catalysts. Milestones in terms of ORR mass activity are created by this type of catalyst. However, the specific synergy between LP and PF moieties has not been well elucidated. Herein, two model catalysts are synthesized, i.e., atomically dispersed Co/N/C supporting Pt single atoms (Co/N/C@Pt-SAs) and PtCo nanoparticles (Co/N/C@PtCo-NPs). Interestingly, the Co/N/C@PtCo-NPs catalyst presents higher ORR mass activity prior to Co/N/C@Pt-SAs. This is theoretically due to the dual "built-in electric field" in Co/N/C@PtCo-NPs: one electric field with a direction from Pt to Co in NPs and another from Pt to Co/N/C; that is, Pt gains higher electron density in Co/N/C@PtCo-NPs than that in Co/N/C@Pt-SAs, thus forming an asymmetric electron cloud, and regulating the adsorption and activation of oxygen-containing species. In addition, the existence of Co significantly decreases the average valence state of PtCo NPs, indicating a stronger affinity between PtCo NPs and Co/N/C substrate, to account for the enhanced stability.

Effectively boosting hydration capacity and oxygen reduction activity of cobalt-free perovskite cathode by K+ doping strategy for protonic ceramic fuel cells

Development of triple-conducting cathode can extend the electrochemically active region to the entire cathode to more effectively promoting oxygen reduction reaction (ORR). Herein, a cobalt-free perovskite Sr1.75K0.25Fe1.5Mo0.5O6−δ (SKFM) was developed as a single-phase triple-conducting cathode material for protonic ceramic fuel cells (PCFCs). Introduction of K into Sr-site leads to a 21.54 % increase in the hydration capacity compared to the undoped Sr2Fe1.5Mo0.5O6−δ (SFM). The bulk diffusion coefficient and surface exchange coefficient of SKFM are 3.8 and 5.2 times higher than those of SFM at 550 °C, respectively. XAS and EPR results demonstrate that the average valence state of Fe and the concentration of surface oxygen vacancies in SKFM are higher than those in SFM. The polarization resistances (Rp) value of SKFM cathode in wet air is 0.06 Ω cm2 at 700 °C, while it is 0.11 Ω cm2 for SFM cathode, which is reduced by 45.5 %, indicating significantly improved ORR activity. The Rp is dominated by the adsorption and diffusion process of oxygen associated with low-frequency part in wet air. The single cell with a configuration of Ni-BZCY4/21-μm-thick BZCY4/SKFM delivers a power output of 1000.8 mW cm−2 in wet H2 at 700 °C and steady operation at 600 °C for a total of 100 h.

Investigation of variety of valence metal ions combinated novel Co‐rich high entropy oxides and its magnetic properties and microstructure

In this work, a series of five spinel-structured oxides were synthesized using a straightforward and effective solid-state methodology. Departing from the conventional design concept, we opted for the substitution of Fe3 + with five metal cations, all possessing trivalent average valence states and equivalent proportions. X-ray diffraction, scanning electron microscope, energy spectrum analyzer, vibrating sample magnetometer were used to detect the phase, micro-structure, element distribution, magnetism of the samples, respectively. The test results show that samples have the spinel structure (Fd3(_)m), and the element composition and distribution are the same as expected. The test results of magnetic properties reveal that these five samples exhibit the properties of soft magnetic materials. The maximum adjustment range of saturation magnetization (Ms) is increased from 23.5 emu/g to 34.8 emu/g by adjusting the elemental composition. Besides, the maximum adjustment range of coercivity (Hc) is increased from 11 Oe to 60 Oe. Furthermore, these materials exhibit a low remanent magnetization ratio, indicating that high-entropy oxides with spinel structures are highly sensitive to changes in an applied magnetic field. The high-entropy oxide is a new material with great prospect. It creates new possibilities for the design of magnetic materials.

Electron Delocalization Realizes Speedy Fenton-Like Catalysis over a High-Loading and Low-Valence Zinc Single-Atom Catalyst.

A zinc (Zn)-based single-atom catalyst (SAC) is recently reported as an active Fenton-like catalyst; however, the low Zn loading greatly restricts its catalytic activity. Herein, a molecule-confined pyrolysis method is demonstrated to evidently increase the Zn loading to 11.54 wt.% for a Zn SAC (ZnSA -N-C) containing a mixture of Zn-N4 and Zn-N3 coordination structures. The latter unsaturated Zn-N3 sites promote electron delocalization to lower the average valence state of Zn in the mix-coordinated Zn-Nx moiety conducive to interaction of ZnSA -N-C with peroxydisulfate (PDS). A speedy Fenton-like catalysis is thus realized by the high-loading and low-valence ZnSA -N-C for PDS activation with a specific activity up to 0.11min L-1 m-2 , outstripping most Fenton-like SACs. Experimental results reveal that the formation of ZnSA -N-C-PDS* complex owing to the strong affinity of ZnSA -N-C to PDS empowers intense direct electron transfer from the electron-rich pollutant toward this complex, dominating the rapid bisphenol A (BPA) elimination. The electron transfer pathway benefits the desirable environmental robustness of the ZnSA -N-C/PDS system for actual water decontamination. This work represents a new class of efficient and durable Fenton-like SACs for potential practical environmental applications.

Cerium geochemical composition of the upper continental crust through time: Implications for tracing past surface redox conditions

To investigate the use of cerium (Ce) in the upper continental crust (UCC) for tracing oxidative weathering, we measured the Ce anomaly (Ce/Ce*), the Ce stable isotope composition (δ142Ce), and the average Ce valence state (Ce#) in twenty-four glacial diamictite composites with depositional ages ranging from ∼2.9 to 0.3 Ga. We observe no distinguishable secular changes in Ce/Ce* (Ce/Ce* = 0.87–0.97) or δ142Ce (−0.092 ± 0.033 to 0.028 ± 0.043‰, 2 S.D.) of the diamictites. Limited elemental partitioning and isotopic fractionation of Ce can be ascribed to the immobilization of REEs, including Ce, in the diamictites during oxidative weathering. We calculated the present-day UCC δ142Ce to be −0.025 (median) ± 0.018‰ (MAD) or −0.029 (mean) ± 0.058‰ (2 S.D.). We assigned average valence state data of Ce (Ce#) in the diamictites into three age groups relative to the timing of the Great Oxidation Event (GOE): pre-GOE (2.9–2.4 Ga; Ce# = 3.09 to 3.22; average of 3.14), syn-GOE (2.4–2.2 Ga; Ce# = 3.18 to 3.73; average of 3.29), and post-GOE ages (0.8–0.3 Ga; Ce# = 3.21 to 3.68; average of 3.36). Our results show distinguishable correlations between Ce# and common weathering (major element ratios and Li isotopes) and redox tracers (e.g., Mn, Mo, V and Th/U) due to increasingly oxidative weathering with time. These results suggest that the valence state of Ce is a sensitive indicator of redox, and advise against relying solely on element- or isotope-based proxies. Combining redox proxies with valence state information can strengthen and complement the interpretation of past redox conditions.

Enhancing the Photocatalytic Activity of Zirconium-Based Metal-Organic Frameworks Through the Formation of Mixed-Valence Centers.

Despite the desirability of metal-organic frameworks (MOFs) as heterogeneous photocatalysts, current strategies available to enhance the performance of MOF photocatalysts are complicated and expensive. Herein, a simple strategy is presented for improving the activity of MOF photocatalysts by regulating the atomic interface structure of the metal active sites on the MOF. In this study, MOF (PCN-222) is hybridized with cellulose acetate (CA@PCN-222) through an optimized atomic interface strategy, which lowers the average valence state of Zr ions. The electronic metal-support interaction mechanism of CA@PCN-222 is revealed by evaluating the photocatalytic CO2 reduction reaction (CO2 RR). The experimental results suggested that the electron migration efficiency at the atomic interface of the MOFs strongly coupled with cellulose is significantly improved. In particular, the CO2 RR to formate activity of CA@PCN-222 photocatalyst greatly increased from 778.2 to 2816.0µmolg-1 compared with pristine PCN-222 without cellulose acetate. The findings suggest that the strongly coupled metal-ligand moiety at the atomic interface of MOFs may play a synergistic role in heterogeneous catalysts.

Fe ion valence states and oxygen vacancies in the La0.5Sr0.5FeO3-γ ferrite under vacuum annealing

The changes in the substituted La0.5Sr0.5FeO3−γ orthoferrite under vacuum annealing in the temperature range of 200–650 °C have been studied by X-ray diffraction analysis, as well as Mössbauer and Raman spectroscopy. Annealing of the as–prepared ferrite with the rhombohedral structure (R3‾c) resulted in its transition to the cubic one (Pm3‾m) at 650 °C. In the as–prepared ferrite being paramagnetic at room temperature, Fe ions were detected in an averaged–valence state between Fe3+ and Fe4+, which was not revealed with a decrease in the temperature down to 85 K. Gradual oxygen loss and an increase in the number of oxygen vacancies took place with an increase in the vacuum annealing temperature. Only Fe3+ ions were present in the ferrite at a vacuum annealing temperature above 500 °C. Several Zeeman sextets in the Mössbauer spectra associated with Fe3+ ions were resulted from the presence of oxygen vacancies and Fe4+ ions in the local environment of Fe3+ ions. The variations in the ratio of the valence states of Fe ions obtained from Mössbauer data depending on a vacuum annealing temperature allowed determining the content of oxygen in all the investigated samples. The contribution of Fe3+ ions that did not have Fe4+ ions and oxygen vacancies in their local environment was shown to increase with a vacuum annealing temperature from 12% (for the as–prepared sample) to 60% (for the sample annealed at 650 °C). On a whole, the process taking place under vacuum annealing can be characterized as a variation of the local environment of Fe3+ ions towards a decrease in its distortion. It was found that the width of the peaks of the Raman spectra decreased and their amplitude increased with an increase in the vacuum annealing temperature, which also demonstrated the improvement of the structural perfection of the samples.

Insights into the full cycling of oxygen in VOCs oxidation on [formula omitted]-MnO2:A NAP-XPS study

α-MnO2-based catalysts are promising materials for VOC oxidation, and understanding how oxygen participates in the reaction is crucial for further improving its catalytic performance. Despite providing many insightful results, oxygen vacancy characterization cannot fully explain the oxygen cycling process, giving sometimes contradictory interpretations. In this paper, NAP-XPS was utilized to investigate the work function and element valence of catalyst surface under reaction conditions. Along with DFT calculation, EELS, and specially designed O2-TPD characterization, we further demonstrated that generating oxygen vacancies will lead to a decrease in the average valence state of Mn elements from Mn4+ to less active Mn3+. Activity data of various VOCs suggest that generating a large number of oxygen vacancies could not enhance the activity of all types of VOC; as for toluene oxidation, replenishing gas-phase oxygen into the bulk phase is also important. This work provides a novel way to explore the metal oxides’ material exchange properties between its surface and gaseous oxygen and paves the way for the rational development of novel and versatile VOC oxidation catalysts.

Fluid Redox Fingerprint of the CaCO3+Antigorite Dehydration Reaction in Subducted Metacarbonate Sediments

Antigorite dehydration is a process able to release, in comparison with other minerals, the highest amount of H2O from a subducting slab. The released fluid delivers critical elements (e.g., S, Cu, and REE) to the overlying subarc mantle, modifying the mantle source of arc magmas and related ore deposits. Whether antigorite breakdown produces oxidising or reducing fluids is debated. Whereas previous studies have investigated antigorite dehydration in serpentinites (i.e., in a (C)AMFS-H2O system), this contribution is devoted to the CMFS-COHS carbonate system, which is representative of the metacarbonate sediments (or carbonate-dominated ophicarbonate rocks) that sit atop the slab. Thermodynamic modelling is used to investigate the redox effect of the carbonate-buffered antigorite dehydration reactions (i.e., brucite breakdown and antigorite breakdown) on electrolytic fluid geochemistry as a function of P-T-fO2. The influence of P-T-fO2 conditions on the solubility of C and S, solute-bound H2 and O2, fluid pH, the average valence states of dissolved C and S, and the fluid redox budget indicates that, in metacarbonate sediments, the CaCO3+antigorite reaction tends to produce reducing fluids. However, the redox state of such fluids is buffered not only by the redox state of the system but also, most importantly, by concomitantly dissolving redox-sensitive minerals (i.e., carbonates, graphite, pyrite, and anhydrite). A qualitative correlation between the redox state of the system and the possible depth of fluid release into the mantle wedge is also derived.

The Interrelation between Iron Valence and Oxygen Vacancies in Substituted Orthoferrite La0.67Sr0.33FeO3– during Heat Treatment

In this paper, we studied substituted lanthanum orthoferrite La0.67Sr0.33FeO3– γ by Mössbauer spectroscopy using X-ray diffraction data. A series of vacuum annealings was performed in the temperature range of tann = 200–650°C, after which no significant changes in the structure of the samples were detected. The Mössbauer measurements at room temperature show that the Fe ions are in an average valence statebetween Fe3+ and Fe4+. Upon vacuum annealing, as the temperature tann increased, the average hyperfine magnetic field on the 57Fe nuclei and the isomer shift of the spectrum increased, which is associated with an increase in the number of vacancies and, accordingly, a decrease in the amount of Fe4+. Mössbauer measure-ments at 85 K showed that the average valence state of iron does not manifest itself. The hyperfine parameters of the low-temperature Mössbauer subspectra obtained from the model interpretation indicate that one of them belongs to Fe4+ ions, and the rest belong to Fe3+. The presence in the spectra of several sextets related to Fe3+ ions is due to the appearance of oxygen vacancies (breaking of the Fe3+–O2––Fe exchange bond) and Fe4+ ions (weakening of the Fe3+–O2––Fe exchange bond) in the nearest ionic neighborhood of Fe atoms. Both factors cause a decrease in the hyperfine magnetic field and a change in the isomer shift of the spectrum. As a result of model interpretation of the Mössbauer spectra, the numbers of oxygen vacancies and Fe4+ ions per formula unit depending on vacuum annealing temperature tann were determined for all samples. It wasshown that at tann above 450°C, the process of oxygen leaving the lattice ends and only Fe3+ ions are detected.

Enhanced ozonation of polystyrene nanoplastics in water with CeOx@MnOx catalyst

The nanoplastics released into the environment pose a critical threat to creatures, and thus it is necessary to remove them. However, their natural decomposition usually takes years or even decades, which raises an imminent demand for an efficient removal technology. Herein we report a core-shell CeOx@MnOx catalyst for enhancing ozonation of polystyrene nanoplastics in water. Ozonation achieves 31.67% molecular weight removal of polystyrene nanoplastics in the first 10 min reaction, which is increased to 51.67% in catalytic ozonation by MnOx and further improved to 73.33% in catalytic ozonation via CeOx@MnOx. The remarkable thing is the CeOx@MnOx could achieve almost 96.70% molecular weight removal after 50 min reaction. The specific catalytic mechanism is ozone decomposes into reactive oxygen radicals (•OH, •O2− and 1O2) after capturing electrons from MnOx, improving the polystyrene nanoplastics removal. Meanwhile, the Mn averaged valence state increases, making it harder to donate electrons to ozone. This can be alleviated by encapsulating the CeOx core in the MnOx, enabling electrons replenishment from the CeOx core to the MnOx shell, which is verified by the experiment and density functional theory calculations. The repeated experiment demonstrates the CeOx@MnOx possesses excellent stability, maintaining 95.25–96.70% removal efficiency of polystyrene nanoplastics. This research provides a possibility for the efficient removal of nanoplastics in water.

Низкотемпературные мёссбауэровские исследования замещенного феррита стронция La-=SUB=-0.67-=/SUB=-Sr-=SUB=-0.33-=/SUB=-FeO-=SUB=-3-γ-=/SUB=-

The valence states of Fe atoms and the formation of oxygen vacancies in substituted La0.67Sr0.33FeO3−γ orthoferrite have been studied in detail by low-temperature Mössbauer spectroscopy under oxygen removal. It has been shown that the averaged valence state of Fe atoms is not revealed with a decreasing measurement temperature. This makes it possible to reveal Fe4+ ions. The Analysis of the obtained data allows us to conclude that the presence of several Zeeman sextets associated with Fe3+ ions is related to the appearance of oxygen vacancies and Fe4+ ions in the nearest ionic surrounding of Fe ions. Using the Mössbauer data, the number of oxygen vacancies and oxygen ions has been determined for all the studied samples depending on the vacuum annealing temperature.

Low-temperature Mossbauer studies of substituted La-=SUB=-0.67-=/SUB=-Sr-=SUB=-0.33-=/SUB=-FeO-=SUB=-3-γ-=/SUB=- lanthanum ferrite

The valence states of Fe atoms and the formation of oxygen vacancies in substituted La0.67Sr0.33FeO3-γ orthoferrite have been studied in detail by low-temperature Mossbauer spectroscopy under oxygen removal. It has been shown that the averaged valence state of Fe atoms is not revealed with a decreasing measurement temperature. This makes it possible to reveal Fe4+ ions. The Analysis of the obtained data allows us to conclude that the presence of several Zeeman sextets associated with Fe3+ ions is related to the appearance of oxygen vacancies and Fe4+ ions in the nearest ionic surrounding of Fe ions. Using the Mossbauer data, the number of oxygen vacancies and oxygen ions has been determined for all the studied samples depending on the vacuum annealing temperature. Keywords: perovskites, substituted lanthanum ferrites, X-ray diffraction analysis, Mossbauer spectroscopy, Fe valence states, oxygen vacancies.

High-Performance Oxygen Evolution Reaction Electrocatalysts Discovered via High-Throughput Aerogel Synthesis

A combinatorial high-throughput aerogel synthesis method is developed to systematically study the synergistic catalytic effects of multiple non-noble metal elements. A large number of aerogels with different compositions were synthesized and the corresponding ternary phase diagrams of the composition–electrocatalytic performance were constructed. A batch of aerogel catalysts with outstanding catalytic performance and stability for the electrochemical oxygen evolution reaction (OER) were discovered. Amorphous Fe3Co3Ni2-(oxy)hydroxide with excellent electrocatalytic performance (Tafel slope of 49 mV dec–1 and η100 of 421.48 ± 6.41 mV) was found to achieve a mass activity of 611.23 A/gmetal at 1.63 V (vs RHE). X-ray photoemission spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) studies reveal that the incorporation of a third atom (Ni and Ce) into the binary aerogels enlarges the Co–O atomic distance and reduces the average valence state of Co, which in turn speed up the oxygen evolution reaction kinetics. This work puts forward a strategy for high-throughput synthesis and screening of electrocatalysts and provides valuable data sets for future machine learning and prediction of high-performance electrocatalysts.

Role of Fe atom valence states and oxygen vacancies in substituted lanthanum ferrite La0.67Sr0.33FeO3-γ

The substituted orthoferrite La0.67Sr0.33FeO3−γ was studied using scanning electron microscopy, X-ray diffraction (XRD), and Mössbauer and Raman spectroscopy. A series of vacuum annealing in the temperature range of 200–650 °C was performed, resulting in negligible changes in the crystal structure of samples. The volume of the pseudocubic unit cell increased continuously with raising temperature up to 450 °C. It follows from the Mössbauer measurements that at room temperature Fe ions were characterized by an averaged-valence state. The vacuum annealing induced oxygen vacancies and changed the averaged-valence state of Fe ions. Sufficiently good correlations among the Mössbauer, XRD, and Raman spectroscopy data were obtained.