Preferential Processing Research Articles

Test-Retest Reliability of Two Computationally-Characterised Affective Bias Tasks

Affective biases are commonly seen in disorders such as depression and anxiety, where individuals may show attention towards and preferential processing of negative or threatening stimuli. Affective biases have been shown to change with effective intervention: randomized controlled trials into these biases and the mechanisms that underpin them may allow greater understanding of how interventions can be improved and their success be maximized. For such trials to be informative, we must have reliable ways of measuring affective bias over time, so we can detect how and whether they are altered by interventions: the test-retest reliability of our measures puts an upper bound on our ability to detect any changes. In this online study we therefore examined the test-retest reliability of two behavioural affective bias tasks (an ‘Ambiguous Midpoint’ and a ‘Go-Nogo’ task). 58 individuals recruited from the general population completed the tasks twice, with at least 14 days in between sessions. We analysed the reliability of both summary statistics and parameters from computational models using Pearson’s correlations and intra-class correlations. Standard summary statistic measures from these affective bias tasks had reliabilities ranging from 0.18 (poor) to 0.49 (moderate). Parameters from computational modelling of these tasks were in many cases less reliable than summary statistics. However, embedding the covariance between sessions within the generative modelling framework resulted in higher estimates of stability. We conclude that measures from these affective bias tasks are moderately reliable, but further work to improve the reliability of these tasks would improve still further our ability to draw inferences in randomized trials.

A domain-general process for theta-rhythmic sampling of either environmental information or internally stored information.

Many everyday tasks, such as shopping for groceries, require the sampling of both environmental information and internally stored information. Selective attention involves the preferential processing and sampling of behaviorally important information from the external environment, while working memory involves the preferential processing and sampling of behaviorally important, internally stored information. These essential cognitive processes share neural resources within a large-scale network that includes frontal, parietal, and sensory cortices, and these shared neural resources can lead to between-domain interactions. Previous research has linked external sampling during selective attention and internal sampling during working memory to theta-rhythmic (3-8 Hz) neural activity in higher-order (e.g., frontal cortices) and sensory regions (e.g., visual cortices). Such theta-rhythmic neural activity might help to resolve the competition for shared neural resources by isolating neural activity associated with different functions over time. Here, we used EEG and a dual-task design (i.e., a task that required both external and internal sampling) to directly compare (i) theta-dependent fluctuations in behavioral performance during external sampling with (ii) theta-dependent fluctuations in behavioral performance during internal sampling. Our findings are consistent with a domain-general, theta-rhythmic process for sampling either external information or internal information. We further demonstrate that interactions between external and internal information-specifically, when to-be-detected information matches to-be-remembered information-are not dependent on theta-band activity (i.e., theta phase). Given that these theta-independent 'match effects' occur during early processing stages (peaking at 75 ms), we propose that theta-rhythmic sampling modulates external and internal information during later processing stages.

Characterizing preferential infiltration of loess using geostatistical electrical resistivity tomography

Preferential infiltration is prevalent in loess and is pivotal in disasters such as landslides. However, the inherent multi-scale heterogeneity of loess makes traditional in-situ monitoring techniques challenging for characterizing the preferential infiltration process. This study employed the Geostatistical Electrical Resistivity Tomography (GERT) to examine the spatial distribution of mass water content (ωs) in loess strata to understand the preferential infiltration processes in loess. This study improved stimulus-response data quality and used GERT to characterize the spatial-temporal distribution of electrical conductivity (σ) and estimate ωs through the σ-ωs relationship. This study indicates that the surface loess layer has higher ωs than deeper layers, rapidly declining as depth increases. Under preferential infiltration, early-stage water forms a spherical saturated zone, transforming into an ellipsoid as it descends. Using equivalent homogeneous parameters as prior information effectively improved σ estimation. This study found a 15.9% error in the total change in water content based on the GERT survey compared to the known amount of injected water. It explores the possible impacts of the uncertainty of the unknown relationship between σ and ωs, its spatial variability, and the accuracy of the survey on the error. The formation of an electric double-layer structure within the loess as the saturation increases, which reduces the sensitivity of GERT to changes in water content, is likely another cause. Finally, these areas are essential for advancing future studies on applying geophysical tools to accurately estimate water distributions in loess formations.

Accelerated CO2 preferential permeation using graphene oxide confined ionic liquid membranes for CO2/H2 separation

Due to the enhanced mass transfer process of nanochannels and the high affinity of ionic liquids (ILs) for carbon dioxide (CO2), the membranes combined with 2D nanosheets and ILs have attracted significant attention in carbon capture, utilization, and storage (CCUS). However, regulating the structure of IL to enhance the separation performance of CO2 remains a big challenge. Herein, we selected different imidazolium-based ILs and proposed a simple strategy to prepare nano-confined IL membranes by intercalating ILs into graphene oxide (GO). These membranes are subsequently used to remove CO2 from industrial syngases, where they display an abnormal CO2 preferential permeation process relative to the smaller H2 molecule. Meanwhile, CO2 permeation decreases gradually with the increase of alkyl chain length, whereas CO2/H2 selectivity shows a tendency to first increase and then decrease. Interestingly, all GO-confined IL membranes surpass the Robeson upper bound, achieving peak CO2 permeance of 13.85 GPU and CO2/H2 selectivity of 13.58, respectively. Further characterization of the interlayer spacing and density functional theory (DFT) calculations reveal that the high CO2/H2 separation performance mainly arises from the fact that nano-confined ILs can block the transit of H2 through the dense packing structure, simultaneously enhancing CO2 solubility and permeability through the membrane. These quantitative insights into the nanoconfined IL membrane not only deepen the scientific understanding of the abnormal transfer process within the nanochannel but also propose novel methodologies for preparing high-performance CO2 capture membranes.

Saccadic "inhibition" unveils the late influence of image content on oculomotor programming.

Image content is prioritized in the visual system. Faces are a paradigmatic example, receiving preferential processing along the visual pathway compared to other visual stimuli. Moreover, face prioritization manifests also in behavior. People tend to look at faces more frequently and for longer periods, and saccadic reaction times can be faster when targeting a face as opposed to a phase-scrambled control. However, it is currently not clear at which stage image content affects oculomotor planning and execution. It can be hypothesized that image content directly influences oculomotor signal generation. Alternatively, the image content could exert its influence on oculomotor planning and execution at a later stage, after the image has been processed. Here we aim to disentangle these two alternative hypotheses by measuring the frequency of saccades toward a visual target when the latter is followed by a visual transient in the central visual field. Behaviorally, this paradigm leads to a reduction in saccade frequency that happens about 90 ms after any visual transient event, also known as saccadic "inhibition". In two experiments, we measured occurrence of saccades in visually guided saccades as well as microsaccades during fixation, using face and noise-matched visual stimuli. We observed that while the reduction in saccade occurrence was similar for both stimulus types, face stimuli lead to a prolonged reduction in eye movements. Moreover, saccade kinematics were altered by both stimulus types, showing an amplitude reduction without change in peak velocity for the earliest saccades. Taken together, our experiments imply that face stimuli primarily affect the later stages of the behavioral phenomenon of saccadic "inhibition". We propose that while some stimulus features are processed at an early stage and can quickly influence eye movements, a delayed signal conveying image content information is necessary to further inhibit/delay activity in the oculomotor system to trigger eye movements.

Revolutionizing multifunctional electrolyte additive design and synthesis for high-voltage nickel-rich batteries in diverse climates

The high-voltage LiNi0.6Co0.2Mn0.2O2 (NCM622) cathode presents a promising avenue for advancing the energy density of lithium-ion batteries. Nevertheless, current limitations primarily arise from electrolyte systems unable to meet stringent criteria, including stable performance under elevated temperatures and efficient discharge at low temperatures. In this study, we address these challenges by designing a molecular structure incorporating boron oxygen functional groups, phenyl-, and fluorine moieties to simultaneously enhance ion conductivity and thermal stability under extreme voltages. A multifunctional electrolyte additive, 3, 4, 5-trifluorophenylboronic anhydride (TFPBA), has been successfully developed via synthesis. TFPBA plays a pivotal role in promoting the formation of a hierarchical cathode electrolyte interphase (CEI) through its preferential decomposition and oxidation processes. This CEI features a mechanically stable inner layer enriched with fluorophenyl- groups, crucial for high-temperature cycling, alongside an outer layer concentrated with BxOyFz complexes that significantly improve Li+ conductivity, ensuring superior performance under low-temperature conditions and at elevated rates. Moreover, TFPBA acts as an HF scavenger within the electrolyte, mitigating corrosive effects on the cathode surface, thereby curtailing CEI reformation and the transition metal dissolution. The Li/NCM622 half cells with TFPBA exhibit impressive capacity retention rates of 92.58%, 80.09%, and 81.77% after extensive cycling at temperatures of −20 °C, 25 °C, and 55 °C, respectively. Moreover, NCM622/graphite full cells with TFPBA achieve a remarkable capacity retention of 97.97% after 150 cycles at room temperature. Our findings highlight the exceptional electrochemical performance of NCM622 cathodes at elevated voltages across a wide temperature range, providing valuable insights for the development of advanced electrolytes in high-demand applications.

Towards a new approach in chiral resolution: Pressurized-CO2 assisted preferential cocrystallization

We here report the first occurrence of a preferential cocrystallization process assisted by compressed carbon dioxide. Our study focuses on the Nefiracetam-Mandelic acid conglomerate forming system. The cocrystal conglomerate was successfully crystallized using compressed CO2 as antisolvent, and acetone, ethyl acetate, or isobutanol as solvents for starting solutions in the so-called GAS process. We then focus on acetone to successfully perform preferential cocrystallization supported by compressed CO2. A critical step in the design of the process is the adaptation of the set-up to allow the introduction of enantiopure seeding inside the reactor. Based on the use of seeded rings, we test several seeding configurations to enhance enantioseparation through the simultaneous crystallization of both enantiomers in two different areas of the reactor.

Visual perceptual learning is enhanced by training in the illusory far space.

Visual objects in the peripersonal space (PPS), are perceived faster than farther ones, appearing in the extrapersonal space (EPS). This shows preferential processing for visual stimuli near our body. Such an advantage should favor visual perceptual learning occurring near, as compared to far from observers, but opposite evidence has been recently provided from online testing protocols, showing larger perceptual learning in the far space. Here, we ran two laboratory-based experiments investigating whether visual training in PPS and EPS has different effects. We used the horizontal Ponzo Illusion to create a lateralized depth perspective while participants completed a visual search task in which they reported whether or not a specific target object orientation (e.g., a triangle pointing upward) was present amongst distractors. This task was completed before and after a training phase in either the (illusory) near or far space for one hour. In Experiment 1, the near space was in the left hemispace, whereas in Experiment 2 it was in the right. Results showed that, in both experiments, participants were more accurate after training in the far space, whereas training in the near space led to either improvement in the far space (Exp. 1), or no change (Exp. 2). Moreover, we found a larger visual perceptual learning when stimuli were presented in the left compared to the right hemispace. Differently from visual processing, visual perceptual learning is more effective in the far space. We propose that depth is a key dimension that can be used to improve human visual learning.

Is processing superiority a universal trait for all threats? Divergent impacts of fearful, angry, and disgusted faces on attentional capture

Fearful, angry, and disgusted facial expressions are evolutionarily salient and convey different types of threat signals. However, it remains unclear whether these three expressions impact sensory perception and attention in the same way. The present ERP study investigated the temporal dynamics underlying the processing of different types of threatening faces and the impact of attentional resources employed during a perceptual load task. Participants were asked to judge the length of bars superimposed over faces presented in the center of the screen. A mass univariate statistical approach was used to analyze the EEG data. Behaviorally, task accuracy was significantly reduced following exposure to fearful faces relative to neutral distractors, independent of perceptual load. The ERP results revealed that the P1 amplitude over the right hemisphere was found to be enhanced for fearful relative to disgusted faces, reflecting the rapid and coarse detection of fearful cues. The N170 responses elicited by fearful, angry, and disgusted faces were larger than those elicited by neutral faces, suggesting the largely automatic and preferential processing of threats. Furthermore, the early posterior negativity (EPN) component yielded increased responses to fearful and angry faces, indicating prioritized attention to stimuli representing acute threats. Additionally, perceptual load exerted a pronounced influence on the EPN and late positive potential (LPP), with larger responses observed in the low perceptual load condition, indicating goal-directed cognitive processing. Overall, the early sensory processing of fearful, angry, and disgusted faces is characterized by differential sensitivity in capturing attention automatically, despite the importance of these facial signals for survival. Fearful faces produce a strong interference effect and are processed with higher priority than angry and disgusted ones.

Reduced processing of afforded actions while observing mental content as ongoing mental phenomena

While consciousness is typically considered equivalent to mental contents, certain meditation practices—including open monitoring (OM)—are said to enable a unique conscious state where meditators can experience mental content from a de-reified perspective as “ongoing phenomena.” Phenomenologically, such a state is considered as reduction of intentionality, the mental act upon mental content. We hypothesised that this de-reified state would be characterised by reduced mental actional processing of affording objects. We recruited two groups of participants, meditators with long-term experience in cultivating a de-reified state, and demographically-matched novice meditators. Participants performed a task with images in two configurations—where objects did (high-affordance) and did not imply actions (low-affordance)—following both a baseline and OM-induced de-reified state, along with EEG recordings. While long-term meditators exhibited preferential processing of high-affordance images compared to low-affordance images during baseline, such an effect was abolished during the OM state, as hypothesised. For novices, however, the high-affordance configuration was preferred over the low-affordance one both during baseline and OM. Perceptual durations of objects across conditions positively correlated with the degree of µ-rhythm desynchronization, indicating that neural processing of affordance impacted perceptual awareness. Our results indicate that OM styles of meditation may help in mentally decoupling otherwise automatic cognitive processing of mental actions by affording objects.

Intra-community link formation and modularity in ultracold growing hyperbolic networks

Hyperbolic network models offer a straightforward yet powerful method for understanding the small-world, scale-free, highly clustered, and modular characteristics typical of complex systems that are often called as real-world networks. These models involve randomly positioning nodes in a hyperbolic space and connecting them based on a probability that diminishes with distance. In this study, we examine the community structure within networks created by the Popularity Similarity Optimization model, a fundamental hyperbolic model, when the temperature parameter (responsible for tuning the clustering coefficient) is set to the limiting value of zero. We focus on link formation within communities and show their close relation with non-linear preferential attachment processes. Based on this, we derive analytical expressions that significantly improve previous estimates of the expected modularity for partitions formed by equally sized angular sectors in the 2d hyperbolic space. Our formulas can now predict average modularity, confirmed by numerical simulations, with high accuracy over a broader range of model parameters and community sizes relative to the whole network. These results advance our understanding of module formation in hyperbolic networks, highlighting the surprising emergence of communities despite the lack of explicit community formation steps in the model definition.

Effectiveness of biological drying for citric acid dewatered sludge: Evaluating the impact of energy-efficient ventilation strategies

The effectiveness of dehydration and utilization processes for citric acid dewatered sludge is hampered by its high concentrations of polysaccharides, proteins, and water-binding properties of microbial extracellular polymers (EPS). This research explores the efficacy and mechanisms involved in extracting water from this type of sludge using biological drying technology, with varying rates of ventilation. Especially pertinent was the use of low ventilation rates as control variables. Our results suggest that a scheduled intermittent ventilation at lower rates allows for the most efficient removal of water, achieving a rate of 41.71 % within eight days, according to the zero-order kinetic model. Remarkably, the peak temperature registered was 60 °C, reaching this threshold in just 0.1 days and maintaining high temperatures for approximately 5.9 days. Component analysis of organic matter illustrated a preferential degradation process for lipids under these ventilation conditions which is pivotal for releasing and transforming bound water for efficient extraction, as well as facilitating the breakdown of easily hydrolysable materials. Further, polysaccharide/protein (EPS) decomposition contributed to water removal, though less significantly. The periodic ventilation strategy allowed for the maximum cumulative temperature to be sustained, demonstrating superior efficiency in harnessing bio-generated heat (82.77 % for water evaporation), resulting in dry sludge suitable for self-sustained combustion at relatively low cost ($26.61/t). Highlighted by this study is the considerable potential of energy-efficient ventilation methods in the biological drying treatment of citric acid fermented sludge and similar industrial waste materials.

Wet oxidation of TiZrHfNbTaV high-entropy alloys: Role of grain-boundary and interdendritic diffusion

Refractory high-entropy alloys (RHEAs) are sensitive to thermal oxidation, significantly restricting their service performance and potential applications. However, the wet oxidation behavior of RHEAs has remained poorly understood despite the potential risk of catastrophic oxidation caused by water vapor. In this study, the oxidation mechanism of an equiatomic TiZrHfNbTaV high-entropy alloy (HEA) has been investigated in a wet atmosphere at elevated temperatures. Synchronous oxidation of all elements occurs at temperatures below 800 °C. At temperatures above 800 °C, preferential oxidation of Nb, Ti, and Zr, and internal oxidation of V occur on HEAs, which are thermodynamically less preferred as compared with oxidations of more reactive Hf and Ta. Experimental and theoretical analyses show that the oxide grain boundaries and substrate interdendritic regions of HEAs act as diffusion pathways for V and oxidizing species during preferential and internal oxidation processes. This work provides a fundamental understanding of the oxidation of multicomponent alloys in wet environments, which is helpful in the development of effective oxidation resistance strategies and innovative surface engineering techniques.

Hydrogeochemical processes as a conditioner of freshwater lenses associated with coastal deposits

AbstractThe aim of this work was to study the processes and factors conditioning the hydrochemistry of freshwater lenses associated with Holocene coastal deposits in an area of the Argentinean Atlantic coast. For this purpose, geomorphological units were mapped and a shallow groundwater monitoring network was established, including pre‐existing boreholes and shallow exploration wells. During the construction of the shallow exploration wells, sediment samples were extracted to determine the texture and mineralogical characteristics. Four samplings were carried out to measure in situ physicochemical parameters and to determine majority ions in the water. The chemical data were analysed considering the associated geomorphology, lithology, water balance and hydrodynamics. The geomorphological and lithological characteristics are the combined factors that favour the preferential rainwater recharge processes. Geoforms with greater topography and extension (continental and coastal dunes) tend to store freshwater lenses, while those with lower topography and little areal extension (sand sheets and beach ridges) have very thin lenses and tend to become salinized. Climate and local water balance are factor that determines that groundwater recharge occurs preferentially in winter. This causes increases in groundwater levels and a decrease in the groundwater EC. On the other hand, mineralogy is a factor that conditions the geochemical processes associated with the water–sediment interaction. Within the main geochemical processes, the dissolution and/or mineral weathering, the dissolution of CO2(g) and ion exchange determine the presence of different hydrochemical facies, where Ca‐HCO3 facies dominates in elevated geoforms, while Na‐Cl in lower ones. The results obtained in this work have provided an understanding of the factors and processes that condition groundwater chemistry in coastal deposits, being of vital importance for the management of water resources.

Neutron imaging of exchange flow between biopore and matrix for Bt versus C horizons

AbstractThe surface coating of biopores plays a pivotal role in mediating mass exchange between the biopore and the soil matrix, ultimately governing preferential flow in structured soils. However, quantitative experiments of the flow exchange dynamics in the soil around an earthworm burrow (drilosphere) are limited. Here, we developed an experimental setup to mimic preferential flow within a biopore while monitoring the water distribution by neutron radiography. The objective was to quantify the evolving water content distribution in the biopore with surrounding drilosphere samples from Bt and C horizons. We hypothesize that the distribution of clay and organic material across biopore surfaces in Bt and C horizons impacts the biopore coating material formation (i.e., composition and thickness), thereby influencing its role in controlling mass exchange during preferential flow events. The experimental setup was proposed for in situ quantification of the preferential flow dynamics in an earthworm burrow (biopore) passing through Bt and C horizons of a Luvisol developed on glacial till. The neutron radiographies were obtained at the NEUtron Transmission Radiography facility of the Paul Scherrer Institut, Villingen. The volumetric water content was quantified by calibrating gray scale values from radiography images with defined water contents using stepped aluminum cuvettes attached to the samples; image analysis was used to determine sorptivity at the biopore–soil matrix interface. The water exchange flow was found to be smaller for coated biopore surface in the more clayey Bt horizon, as compared to the coarser textured carbonaceous subsoil C horizon, where higher sorptivity intensified mass exchange. The method most realistically captured the dynamics of the vertical preferential flow process in a biopore, including lateral exchange flow, by determining the water sorptivity of the drilosphere. In contrast to mini‐infiltrometer data, biopore–matrix exchange flow was here more restricted for Bt in contrast to carbonaceous C horizon. Since both horizons showed the presence of coating material on their burrow walls, the results suggest further analysis of their contrasting properties and structures.

Attentional Bias of Individuals with Social Anxiety towards Facial and Somatic Emotional Cues in a Holistic Manner.

Attentional bias towards threatening information is a crucial factor contributing to the development and persistence of social anxiety. However, the attentional bias towards threat information and the preferential processing pattern of emotional cues in individuals with social anxiety disorder during integrated facial and physical stimuli processing remain unclear. In this study, we employed a dot-probe paradigm to investigate the attentional bias towards integrated emotions (facial-body) among students with high and low levels of social anxiety (Experiment 1). Experiments 2 and 3 examined the attentional bias of socially anxious individuals when faced with conflicting emotional cues from faces or bodies in relation to integrated emotions. The data revealed that participants both high and low levels of social anxiety participants exhibited accelerated orienting and biased attention towards facial-body emotional processing. When there was inconsistency between emotional cues from faces or bodies and integrated emotions, higher levels of social anxiety were associated with increased vigilance towards threatening faces or bodies. These findings underscore that individuals with social anxiety possess an ability to rapidly capture threatening cues during the processing of facial-body emotional stimuli while also demonstrating a tendency to avoid relying solely on facial cues by compensating through bodily cues for emotion perception.

Emotional T2 attenuates attentional blink: A window to understanding the preferential processing of emotion

Emotional T2 attenuates attentional blink: A window to understanding the preferential processing of emotion

Functional magnetic resonance imaging study of group independent components underpinning item responses to paranoid-depressive scale.

Our study expand upon a large body of evidence in the field of neuropsychiatric imaging with cognitive, affective and behavioral tasks, adapted for the functional magnetic resonance imaging (MRI) (fMRI) experimental environment. There is sufficient evidence that common networks underpin activations in task-based fMRI across different mental disorders. To investigate whether there exist specific neural circuits which underpin differential item responses to depressive, paranoid and neutral items (DN) in patients respectively with schizophrenia (SCZ) and major depressive disorder (MDD). 60 patients were recruited with SCZ and MDD. All patients have been scanned on 3T magnetic resonance tomography platform with functional MRI paradigm, comprised of block design, including blocks with items from diagnostic paranoid (DP), depression specific (DS) and DN from general interest scale. We performed a two-sample t-test between the two groups-SCZ patients and depressive patients. Our purpose was to observe different brain networks which were activated during a specific condition of the task, respectively DS, DP, DN. Several significant results are demonstrated in the comparison between SCZ and depressive groups while performing this task. We identified one component that is task-related and independent of condition (shared between all three conditions), composed by regions within the temporal (right superior and middle temporal gyri), frontal (left middle and inferior frontal gyri) and limbic/salience system (right anterior insula). Another component is related to both diagnostic specific conditions (DS and DP) e.g. It is shared between DEP and SCZ, and includes frontal motor/language and parietal areas. One specific component is modulated preferentially by to the DP condition, and is related mainly to prefrontal regions, whereas other two components are significantly modulated with the DS condition and include clusters within the default mode network such as posterior cingulate and precuneus, several occipital areas, including lingual and fusiform gyrus, as well as parahippocampal gyrus. Finally, component 12 appeared to be unique for the neutral condition. In addition, there have been determined circuits across components, which are either common, or distinct in the preferential processing of the sub-scales of the task. This study has delivers further evidence in support of the model of trans-disciplinary cross-validation in psychiatry.

Sphere-Confined Reversible Zn Deposition for Stable Alkaline Aqueous Batteries.

The practical applications of alkaline zinc-based batteries are challenged by poor rechargeability with an insufficient zinc utilization ratio. Herein, a sphere-confined reversible zinc deposition behavior from a free-standing Zn anode is reported, which is composed of bi-continuous ZnO-protected interconnected and hollowed Zn microspheres by theKirkendall effect. The cross-linked Zn network with in situ formed outer ZnO shell and inner hollow space not only inhibits side reactions but also ensures long-range conductivity and accommodates shape change, which induces preferential reversible zinc dissolution-deposition process in the inner space and maintains structural integrity even under high zinc utilization ratio. As a result, the Zn electrode can be stably cycled for 390h at a high current density of 20mA cm-2 (60% depth of discharge), outperforming previously reported alkaline Zn anodes. A stable zinc-nickel oxide hydroxide battery with a high cumulative capacity of 8532 mAh cm-2 at 60% depth of discharge is also demonstrated.

Unravelling the micro-mechanism of oxygen reduction reaction on Fe–N4 embedded in graphene

We conducted a first-principles density functional study on the FeN4 embedded in graphene (Fe–N4-Gra) for the Oxygen Reduction Reaction (ORR). Our study unraveled certain microscopic characteristics of the ORR process on the catalyst that are not readily observable in experiments. Firstly, we investigated the reduction preferences of the two oxygen atoms in the side-on form of O2. Our findings indicate that the 2p orbital of the Ob atom, located further from the central Fe atom, exhibits a significantly stronger overlap with the Fe 3d orbital compared to the Oa atom adjacent to Fe. This suggests a preferential reduction process occurring on the Ob atom. The Löwdin charge distribution between the two atoms further supports this observation. Secondly, we demonstrated that minimizing the orbital energy gap and enhancing the hybridization or resonance between the Fe-3d and O-2p orbitals is the origin of the activity of the Fe–N–C catalyst. We propose that future catalyst designs should consider expanding the Fe 3d or 4s orbital to overlap with the (σ2p)* orbital of O2 in order to achieve higher efficiency of 4 electron reduction process. These findings contribute to a deeper understanding of the ORR process on the Fe–N4-Gra catalyst and provide valuable insights for the development of more efficient catalysts in the future.