Reactive Surface Area Research Articles

Editorial overview: Porous electrodes for energy applications

Porous electrodes are essential and high-performance components, which determine the performance of batteries, fuel cells, electrolysis cells, and further electrochemical devices. Improving their performance is a complex endeavor as the situation inside the electrodes is hard to grasp and control. This special collection brings together a series of valuable contributions regarding advanced experimental investigations and modeling studies of porous electrodes used in electrochemical devices for energy applications. Porous electrodes should provide a sufficiently large surface area for the catalyzed reactions. Very often, the solid porous structure consists of several materials with very different functions such as catalytic activity and electronic or ionic conductivity. The pore system of these electrodes must be optimally designed for the transport of the various reacting species through diffusion, migration, and convection. Moreover, the presence of different phases (liquid electrolytes, gases) in the porous solid matrix of the electrodes leads to an extremely high complexity of the occurring processes. Obviously, there is a great need for improved experimental techniques for the determination of transport parameters and the precise characterization of the porous electrode structures. Based on this information, the development of detailed physicochemically based electrode models will allow for an optimal design of the porous electrodes with even better performance of energy-related electrochemical devices. The overall 11 contributions in this collection cover different electrochemical applications such as lithium-ion batteries, carbon dioxide electrolysis, fuel cells, supercapacitors, and solar cells. In addition to experimental studies devoted to the characterization of the pore system and the determination of important performance parameters, improved models for electrodes and cells are another focus of this special issue. As guest editors appointed by Electrochemical Science Advances, we would like to thank all authors for their valuable contributions, the reviewers for their thoughtful comments, and the publisher Brian P. Johnson for his kind support. We do hope that this special collection on porous electrodes will provide some useful insights for the future development of improved technologies for energy storage and conversion. The authors declare no conflict of interest.

Interfacial Regulation of ZIF-67 on Bacteria to Generate Bifunctional Sensing Material on Chip for Qualifying Cell-Released Reactive Oxygen Species.

Cell's activities are highly dependent on signal molecules, of which reactive oxygen species of the superoxide anion (O2•-) and hydrogen peroxide (H2O2) are important ones that always work together to regulate biological processes such as apoptosis and oxidative stress. It is of significance to realize simultaneous qualification of O2•- and H2O2 but it still faces challenges particularly in live-cell assay with a complex environment. We report the design of a bifunctional sensing material by interfacially regulating ZIF-67 on bacteria Shewanella putrefaciens to generate cobalt nanoparticles/nitrogen-doped porous carbon nanorods (Co/N-doped CNRs) and its sensing chip for qualifying cell-released O2•- and H2O2. Co/N-doped CNRs exhibit unique properties including porous structure for significantly increased reaction surface area and coordinating Co nanoparticles for rich active sites. The bifunctional Co/N-doped CNRs is used to fabricate the electrochemical sensing chip, which achieves a fast response time (0.5 s for O2•-, 1.9 s for H2O2), a low detection limit (0.69 nM for O2•-, 2.25 μM for H2O2), and a remarkably high sensitivity (792.30 μA·μM-1·cm-2 for O2•-, 153.91 μA·mM-1·cm-2 for H2O2), among the best of reported bifunctional nanozymes.

In Situ Detection of Electrochemical Reaction Surface Area by Optical Weak Measurement.

The surface area is key to electrochemical systems, including those in electrocatalysis and energy storage. Studies have shown that the surface area of the electrocatalyst directly affects the electrochemical activity, adsorption performance, and stability of the electrocatalyst. This paper used an optical weak measurement (WM) method, which has little impact on the analyte, to measure the reaction surface area (RSA) that actually participated in the electrochemical reaction. Then compared the RSA obtained by the WM with the total surface area (TSA) obtained by the standard Brunauer-Emmett-Teller (BET) measurement and the active surface area (ASA) obtained by the electrochemical double-layer capacitance (EDLC) method. Their growth trend was consistent, indicating the reliability of the WM method. Compared with the above two methods, the WM method is an in situ detection and easy to operate experimentally, which can help researchers to consider the effect of surface area on electrocatalyst performance more rationally.

Reconciling predicted and observed carbon mineralization in siliciclastic formations

The study of natural CO2 storage reservoirs has demonstrated that carbon mineral trapping is the safest mechanism for subsurface CO2 storage. The slow rate of fluid-rock reactions makes it imperative to use reactive transport simulations as a tool for estimating reservoir scale carbon mineral trapping capacities. However, there is often a disparity in the estimations of carbon mineral trapping capacities determined from reactive transport simulations and recorded in natural CO2 storage reservoirs. This might be due to several factors such as the uncertainty around simulations parameters such as mineral reactive surface areas as well as the neglect of sub-core scale lithological heterogeneity in reservoir scale simulations. This study points to the importance of the latter to reconcile the mismatch. Multiphase reactive transport simulations were run on a cm-scale resolution geological model (CRM) of the Paaratte Formation, Otway Basin (Australia), where mm- to cm-scale lithological heterogeneity is incorporated via upscaled rock parameters. Simulations were also run on a m-scale resolution model (MRM) of the same transect to quantify the difference in the predicted secondary mineral composition due to the incorporation of sub-core scale heterogeneity in reservoir scale simulations. The simulation outcomes for both the models were compared to the data from the Pretty Hill Formation, a natural CO2 storage analogue within the Otway Basin with similar primary mineral composition. The results from the CRM compare well with the secondary carbonate mineralogy of the Pretty Hill Formation. In contrast, the MRM strongly underestimates carbonate mineral formation. The results highlight that the incorporation of mm- to cm-scale lithological interfaces in reservoir scale reactive transport simulations can increase carbon mineralization estimates in siliciclastic formations by 3–6 orders of magnitude as these interfaces are sites for mineral precipitation.

Estimation of Mineral Accessible Surface Area from Mineral Abundance and Clay Content

The mineral reactive surface area is often quantified through a wide range of approaches (e.g., Brunauer–Emmett–Teller adsorption, geometry approximation, and imaging techniques). As such, values vary 1–5 orders of magnitude which can result in large discrepancies when used in reactive transport models to simulate geochemical reaction rates. Simulations carried out using mineral accessible surface areas (ASAs) determined from a coupled 2D and 3D imaging approach have shown better match with reaction rates measured in core-flood experiments. However, such image processing requires large amounts of time and resources. In this work, the possibility of estimating mineral ASAs from easily measured properties like mineral abundance and porosity is explored. Six sandstone samples of varying compositions were studied along with data from three additional samples from the previous literature. Mineral ASAs were quantified using a combined 2D scanning electron microscopy and 3D X-ray nano-computed tomography imaging approach. Sample properties like mineral accessibility, mineral ASAs, connected porosity, and clay content were compared to explore potential correlations between properties. Overall, it was observed that mineral accessibility can be predicted where feldspar mineral accessibility generally increases with increasing abundance and quartz accessibility decreases with increasing clay content. Mineral ASAs vary between samples, depending on the relative abundance of minerals and overall pore connectivity. While the ASA of quartz decreases with abundance, albite and carbonate mineral ASAs increase with abundance. Quantitative observations, including predictive relationships for ASAs from porosity and mineral volume fraction, are developed. Estimations of ASAs and mineral accessibility from more easily quantifiable properties can largely reduce the required extent of image analysis.

A constitutive framework for rocks undergoing solid dissolution

We formulate a time-dependent damage theory for rocks subjected to mechanical deformation and solid dissolution. The constitutive description is inspired by the transition state theory, which states that the rate of dissolution is a function of the reactive surface area measured through the crack density in the volume. We use a gradient-enhanced damage framework in which damage depends on the deformation of the material as well as on the amount of solid mass dissolved over time. The gradient-enhanced formulation is characterized by a three-field variational formulation with the solid displacement, nonlocal equivalent strain, and nonlocal rate of solid dissolution as the basic state variables. Traditionally, time-independent damage theories have only allowed damage to increase with increasing external load. In the proposed framework, the degree of damage may increase due to solid dissolution even when the external load is held fixed. In this way, solid dissolution is viewed as a process that is responsible for bringing about rate-dependent effects such as creep and stress-relaxation, which are two common features of geomaterial behavior.

Flexible nanosheets for plasmonic photocatalysis: microwave-assisted organic synthesis of Ni-NiO@Ni2CO3(OH)2 core-shell@sheet hybrid nanostructures.

Visible light-active nickel-based plasmonic photocatalysts provide a cost-effective alternative to noble metals. However, their rarity, fragility, and limited understanding pose challenges. This work presents a microwave-assisted organic synthesis of a Ni-NiO@Ni2CO3(OH)2 core-shell@sheet plasmonic photocatalyst. By employing time and power dependent synthesis, this catalyst exhibits flexible Ni2CO3(OH)2 nanosheets enveloping the Ni-NiO structure, surpassing the pristine Ni@NiO/NiCO3 core-shell counterpart. Chemical reaction mechanisms suggest that irradiation of pristine Ni-NiO/NiCO3 nano structures leads to breakage of amorphous NiCO3 to Ni2+ and CO32-, which further, in the presence of water solvent, interacts with OH- ions leading to the formation of Ni(CO3)·Ni(OH)2. With enhanced light absorption and photocatalytic properties, the resulting core-shell@sheet photocatalyst demonstrates double the hydrogen evolution reaction yield (40 μmol g-1 h-1) compared to the pristine catalyst (20 μmol g-1 h-1). The enhanced H2 yield is attributed to the flexible sheets, cross-dimensional photocatalyst structure, increased surface area for surface reactions, and higher H2 activity of Ni2CO3(OH)2. This research showcases the potential of microwave-assisted synthesis in developing flexible nanosheets with superior solar water splitting performance.

Life cycle assessment on calcium zincate production methods for rechargeable batteries

The world's energy transition from fossil to renewable energy is unthinkable without further research in energy storage. Decreasing the environmental impacts from the production of energy storage technologies is essential for achieving a green energy transition. Calcium Zincate (CAZN) is used as active material in rechargeable zinc-based batteries (and other products, such as heterogeneous catalysts for biodiesel or antifungal products). They present a low-cost, safer, alternative to Lithium based batteries and are targeted as replacement solutions for lead-acid batteries.We propose a novelty in the synthesis of CAZN, the hydro-micro-mechanical process (HMMS). The residence time of this new route is about 20 times lower than the traditional processes, so its production needs less infrastructure and can deliver quicker at an industrial scale. In addition, laboratory tests indicate that HMMS CAZN has more reaction surface area and the activation of the battery is 1.77 times faster.Using the life cycle assessment (LCA) method, we compare this new process with the current best option, hydro-thermal synthesis (HTS). The cradle-to-gate results per kg of CAZN already indicates that HMMS is an environmentally better alternative for all indicators; especially when considering the normalization of the results with the residence time and the surface area, HMMS delivers better results, with improvements of 97 % in global warming, for instance. With this, we demonstrate that, outside of the cradle-to-gate, variables that make the final products better service units or give more function should be considered as valuable additional information when deciding among alternatives. This also highlights the importance of life cycle thinking when working with chemical processes and substances.In the sensitivity analysis, we developed 7 scenarios related to the energy demand of the processes, and we incorporated the projection in the European electricity mix for 2030 and 2050.

Xylanase production by Trichoderma virens MLT2J2 under solid-state fermentation using corn cob as a substrate

Abstract. Istiqomah L, Cahyanto MN, Zuprizal. 2022. Xylanase production by Trichoderma virens MLT2J2 under solid-state fermentation using corn cob as a substrate. Biodiversitas 23: 6530-6538. Xylanase is one of non-starch polysaccharide (NSP) degrading enzyme encompass in industrial application like animal feed, food, biofuel, and textile. The objective of this study was to produce and characterize the crude xylanase from MLT2J2 isolate that isolated from coconut husk. Molecular identification revealed that MLT2J2 isolate was identified as Trichoderma virens. The xylanase was produced from Trichoderma virens MLT2J2 (108 spores/g of corncob) using corn cob as substrate with 80% initial moisture content using under solid-state fermentation (SSF) at 30°C for 7 d of incubation. Changes in surface morphology and structure of fermented corn cob were monitored by Scanning Electron Microscope (SEM). Statistical analysis was performed using One-way of analysis of variance (ANOVA) followed Tukey Kramer post hoc test to compare treatment means. Under fermentation parameters the maximum xylanase activity was 181.22 U/g-IDW, loss of dry matter 11.43%, and pH was decreased (4.11) at 5 d of incubation compared to initial pH (5.47). Xylanase was produced between a broad range pH 3-8 and showed acidophilic and mesophilic characteristics (optimum at pH 5,0 and 40°C), and also conserved more than 50% of activity before 4 h of incubation at 30°C and after 5 h at 40°C. The micrographs surface of corn cob before SSF appeared intact and smoother, while turned coarser after SSF, suggestive of a disrupted and more porous surface. These findings reveled that T. virens MLT2J2 could produce extracellular xylanase and potential to disrupt the cell wall of corn cob as a cheap substrate for enzyme production thereby increased the reactive surface area of corn cob for enzymatic in situ hydrolysis.

Multi-walled carbon nanotubes derived graphene nanoribbons for high performance supercapacitor applications

This study delineates the supercapacitive performance of multi-walled carbon nanotubes derived nanoribbons. Acid-processed carbon nanotubes were exfoliated and reduced with microwaves to yield high quality graphene nanoribbons (GNRs). Morphological and spectroscopic investigations revealed the successful preparation of graphene nanoribbons from carbon nanotubes. The three electrode system configuration with microwave exfoliated graphene nanoribbons (MWGNRs) based working electrode and H2SO4-PVA gel electrolyte has shown high specific capacitance of 404 F/g at 2 mVs−1 scan rate. This three electrode configuration showed 97.3% of initial capacitance retention after 10,000 cycles, which proves good cycle stability and retention capability of the MWGNRs based electrode with gel electrolyte. A supercapacitive device with MWGNRs based electrodes and 1 M H2SO4 –PVA gel electrolyte was fabricated and tested, which also showed high supercapacitive performance. MWGNRs have more number of reactive edges and high specific surface area as compared to pristine carbon nanotubes and therefore exhibit high specific capacitance. The proposed method is highly scalable and can pave a way to develop high performance low cost supercapacitors.

Effect of Thermal Treatment of Symmetric TiO2 Nanotube Arrays in Argon on Photocatalytic CO2 Conversion

Symmetric titania nanotube arrays (TiO2 NTs) are a well-known photocatalyst with a large surface area and band edge potentials suitable for redox reactions. Thermal treatment of symmetrical arrays of TiO2 nanotubes in argon was used to change the carbon content of the samples. The influence of the carbon content in the structure of symmetrical TiO2 NTs on their photoelectrochemical properties and photocatalytic activity in the conversion of CO2 into organic fuel precursors has been studied. The structure, chemical, and phase composition of obtained samples were studied by X-ray analysis, Raman spectroscopy, and SEM with energy dispersive analysis. It is established that carbon-related defects in the samples accumulate electrons on the surface required for the CO2 conversion reaction. It has been shown for the first time that varying the carbon content in symmetric TiO2 NTs arrays by annealing at different temperatures in argon makes it possible to control the yield of methane and methanol in CO2 conversion. It is revealed that too high a concentration of carbon dangling bonds promotes the growth of CO2 conversion efficiency but causes instability in this process. The obtained results show a high promise of symmetric carbon-doped TiO2 NTs arrays for the photocatalytic conversion of CO2.

A combined experimental and modelling study of granite hydrothermal alteration

Geochemical reactions can induce significant changes of rock reservoir porosity and permeability via mineral dissolution and precipitation processes, affecting the long-term fluid behaviour within various geological systems. The understanding and quantification of these reactions rely on field and experimental studies and on the predictions of reactive transport models.The present study was aimed at assessing the extent to which current geochemical models integrating available mineral dissolution/precipitation rate equations can reproduce the experimental data obtained from 4 to 17-day long hydrothermal alteration experiments of a muscovite-biotite granite and, thus, help provide an accurate description of the evolution of geothermal systems within granitic reservoirs. The experiments were conducted at a constant temperature of 180 °C and over an aqueous fluid pH range of 2 to 8.5, using both mixed-flow and static batch reactors. Modelled major element (K, Al, Si, Ca, and Mg) concentrations were generally in satisfactory agreement with the corresponding measured elemental fluxes – the differences between modelled and experimental values were generally within a factor of 5 – and the predicted identity and mass of formed secondary phases were consistent with the microscopic observations of the reacted solids. However, larger differences between measured and modelled element concentrations were observed when significant amounts of secondary phases formed, notably at pH 2 to 3, and for longer-term batch experiments. Much of this concentration difference stems from the underestimation of the amounts of Al-phases formed at acid to near-neutral pH. Although an idealized rock composition was considered, the observed mismatch between model calculations and experimental data can be attributed to inadequate mineral precipitation reaction rates and a poor description of reactive surface areas in existing geochemical modelling codes. More accurate quantification of precipitation kinetics, including nucleation and growth, and improved descriptions of the temporal change of mineral surface area would enhance the predictive capabilities of reactive transport models and benefit, particularly, the efforts aimed at increasing the sustainability of EGS reservoirs.

Degradation of microcystin algal toxin by 3D printable polymer immobilized photocatalytic TiO2

Novel and sustainable solutions are needed for surface water treatment. Photocatalytic TiO2 is studied but is not directly deployable into natural water bodies due to settling and poor recoverability. This research capitalizes on a convergence of the emerging technologies of 3D printing biocompatible polymer (polylactic acid, PLA) composites, nanotechnology, and advanced oxidative processes to immobilize TiO2 into customizable, high surface area, deployable, and retrievable structures with localized kinetic specificity for harmful algal blooms (HAB). PLA-TiO2 composites at varying loadings (3–34 %) were extruded as feedstock for fused filament fabrication (FFF) enabling low cost printing design freedom of photocatalyst structures (disks, lattices). Large surface area, 3D lattices were printed as PLA composites with highly loaded (34 % w/w) TiO2. Prior to HAB cyanotoxin experiments, the photocatalytic performance of the 3D printed PLA-TiO2 lattice composites (t1/2 = 0.8 h) under UV light were confirmed comparable to free TiO2 (t1/2 = 0.9 h). Under environmentally relevant solar simulation, photocatalysis by printed lattices successfully reduced microcystin (MC) cyanotoxin (t1/2 = 3 h) faster than photolysis alone (t1/2 = 36 h). Lattice mediated photocatalysis of MC in presence of cyanobacteria cells (t1/2 = 11 h) was faster than photolysis (t1/2 = 58 h) but slower than water-only treatment due to cell activity and light attenuation. PLA-TiO2 reduces local pH, promoting MC adsorption and degradation. This research is foundational to novel photocatalytic composite optimization for reactive surface area prototyping enabled by 3D printing and scale-up for sustainable water treatment structures, with applicability to traditional and emerging contaminants.

Green synthesis of biodiesel from microalgae cultivated in industrial wastewater via microbubble induced esterification using bio-MOF-based heterogeneous catalyst

Conventional homogeneous catalysts are non-biodegradable, requiring complicated downstream separation, further diminishing the overall economics. In this paper, a new heterogeneous catalyst, a metal-organic framework modified by biomaterials (Bio-MOF), complexed with an ionic liquid ([HMIM][HSO4]/Bio-MOF), has been synthesized and integrated with microbubble mediated mass transfer technology to overcome the challenges of low conversion. The ionic liquid 1-methylimidazole hydrogen sulfate provides enhanced reactivity, while the Bio-MOF provides more active sites for the reaction. Detailed kinetic analysis suggests the biodiesel production reaction occurs on the vapor/liquid (microalgae oil) interface. The results revealed a higher conversion of (molar ratio of oil: methanol =1: 15, catalyst loading = 0.5 wt% of MO, temperature = 70 ºC) 92 ± 4% was achieved in 30 min relative to acid-catalyzed biodiesel production. Along with higher reactivity and larger surface area provided by the catalysts, the unprecedented higher conversion and rate of reaction is attributed to the “local” excess of alcohol present at the interface and simultaneous removal of water from the reactor. The results of activation energy (7.9 kJ mol−1), enthalpy (4.92 kJ mol−1), entropy (−287 J mol−1), and Gibbs free energy (103.58 kJ mol−1) show that current process required less energy is required for biodiesel production. The catalyst was recycled seven times and showed high stability with little reduction in its activity over these seven runs. The study demonstrates that this newly developed catalyst provides a high reaction rate and conversion of biodiesel production from microalgae oil using a heterogeneous catalyst by integrating it with microbubble-mediated mass transfer.

Heterojunction effect of three-dimensional porous CuFe2O4/CuO for thermal-light excited carriers separation in promoting peroxymonosulfate activation and inhibiting metal ion spillover

CuFe2O4/CuO (CC) heterojunctions with three-dimensional porous structures were prepared by polymer-assisted freeze-drying as visible light (Vis)-peroxymonosulfate (PMS) activators given the good light absorption, efficient charge separation, and high-quality mass transfer characteristics. The heterojunction had Z-scheme interface contact and presented composition-dependent behaviors in enhancing tetracycline hydrochloride (TCH) degradation (∼91.1 % within 36 min for the best ratio) and inhibiting the Cu (155 μg/L) and Fe (5 μg/L) ions spillover. The comparisons of the catalyst/Vis/PMS, catalyst/Vis, and catalyst/PMS systems demonstrated that the heterojunction could separate the light excited electron-hole pairs and thermally generated intrinsic carriers simultaneously. Then, the thermal-light excited carriers could directly participate in the PMS activation process and promote the charge separation and transfer in turn, resulting a higher synergy index of the heterojunction in the CC/Vis/PMS system (7.3) than in the CC/Vis system (4.8). Because visible light has much stronger excitation power than thermal excitation at room temperature, the synergy index of the heterojunction in the CC/Vis/PMS system is also higher than the CC/PMS system (1.9). The PMS activation from thermal-light excited carriers also inhibited the leaching-related surface reactions contributing for the extremely small metal ions spillover. In addition, the porous structure provided a high specific surface area for surface reactions and interconnected channels for mass transfer, while the self-supporting structure can be directly separated from aqueous system for recycling in water treatment process. The new insights on the carriers’ behavior in PMS activation could provide some new ideas for developing high efficient catalyst/Vis/PMS system for wastewater treatment in future.

Polyesters Incorporating Gallic Acid as Oxygen Scavenger in Biodegradable Packaging.

Biodegradable polyesters polybutylene succinate (PBS) and polybutylene adipate-co-terephthalate (PBAT) were blended with gallic acid (GA) via cast extrusion to produce oxygen scavenging polymers. The effects of polyesters and GA contents (5 to 15%) on polymer/package properties were investigated. Increasing GA formed non-homogeneous microstructures and surface roughness due to immiscibility. GA had favorable interaction with PBAT than PBS, giving more homogeneous microstructures, reduced mechanical relaxation temperature, and modified X-ray diffraction and crystalline morphology of PBAT polymers. Non-homogenous dispersion of GA reduced mechanical properties and increased water vapor and oxygen permeability by two and seven folds, respectively. Increasing amounts of GA and higher humidity enhanced oxygen absorption capacity, which also depended on the dispersion characteristics of GA in the matrices. PBAT gave higher oxygen absorption than PBS due to better dispersion and higher reactive surface area. GA blended with PBAT and PBS increased oxygen scavenging activity as sustainable active food packaging using functional biodegradable polymers.

Designing Modular Assembly of Electrochemical Flow Microreactor as an Enabling Technology of Electrosynthesis in Laminar Flow

AbstractFlow microreactors are well‐suited for organic electrosynthesis because they provide a large surface area for reactions and enable precise control of the residence time. Here, we developed three novel electrochemical flow microreactors for organic electrosynthesis: undivided, divided, and electrophotochemical reactors. These flow reactors were easily assembled using modules made of solvent‐resistant plastics and feature high interchangeability of each component and the applicability of a reference electrode. We evaluated our reactors on the basis of the redox response of ferrocene and ferrocenemethanol. The results suggested that the reactors maintain laminar flow with both aqueous and nonaqueous electrolytes. We applied these reactors to paired electrosynthesis and electrophotocatalysis, demonstrating the utility of these systems for electrosynthesis in a laminar flow.

Impact of Porous Microstructure on Performance of Redox Flow Batteries: A Modeling Study

Electrodes are essential components of redox flow batteries (RFBs) that determine performance. Given the advances in 3D printing technologies, bottom-up design and manufacturing electrodes with controllable and reproducible properties can be attainable. In this study, pore network modeling is utilized to understand the coupled transport and reaction processes in Hydrogen-Bromine (H2/Br2) flow batteries. This study highlights the importance of the microstructure while designing a 3D printable microstructure. The 3D pore-scale model is validated against the experimental measurements using an unstructured pore network, extracted from a tomography scan of a commercial carbon paper. A printable ordered cubic lattice with the same permeability as carbon paper increases the maximum power density by 35% due to lower tortuosity and higher mass transport. A parametric study is carried out to understand the role of microstructure, such as pore size, throat size, anisotropy, and lattice unit size, for flow-through and interdigitated flow fields. It is shown that a smaller lattice unit, increases the reactive surface area, lowers the activation and mass transport overpotentials, and consequently enhances the performance of the battery. An improved microstructure design for both flow fields is proposed that intensifies the performance of the battery via engineering the flow path of the electrolyte.

Conductivity-enhanced porous N/P co-doped metal-free carbon significantly enhances oxygen reduction kinetics for aqueous/flexible zinc-air batteries

Heteroatom-doped metal-free carbon catalysts for oxygen reduction reactions have gained significant attention because of their unusual activity and economic cost. Here, a novel N/P co-doped porous carbon catalyst (NPPC) with a high surface area for oxygen reduction reaction (ORR) is constructed by a facile high-temperature calcination method employing ZIF-8 as the precursor and red phosphorus as the phosphorus source. In particular, ZIF-8 is firstly calcined to obtain N-doped carbon (NC) followed by further calcination with red phosphorus to obtain NPPC. Ultraviolet photoelectron spectroscopy (UPS) analysis shows that the ultra-low amount of P doping could significantly decrease the work function from 4.32 to 3.86 eV. The resultant catalyst exhibits a promising electrocatalytic activity with a half-wave potential (E1/2) of 0.87 V and a limiting current density (JL) of 5.15 mA cm−2. Besides, it also shows improved catalytic efficiency and excellent durability with a negligible decay of JL after 2000 CV cycles. Moreover, aqueous and solid-state flexible zinc-air batteries (ZAB) using the catalyst show a promising application potential. This work provides new insight into developing P/N-doped metal-free carbon ORR catalysts.

Influence of Different Pretreatment Methods and Conditions on the Anaerobic Digestion Efficiency of Spent Mushroom Substrate

Consumption of mushrooms has recently increased due to their health benefits; consequently, increased mushroom cultivation generates large volumes of spent mushroom substrate (SMS) and effective methods for SMS valorization are thus required. Anaerobic digestion (AD) processes SMS with minimal energy and reduces the amount of waste generated; moreover, it contributes to energy generation through biogas production. To improve the energy efficiency of AD and promote sufficient biomass pretreatment, thermal pretreatment conditions require further investigation. Here, we evaluated the pretreatment efficiency and biogas production of the SMS thermal pretreatment process, studying different pretreatment temperatures to understand the formation of SMS degradation products and the changes in AD efficiency. Particularly, mechanical and hydrothermal pretreatment (HTP) methods were employed to improve SMS biodegradability. By increasing the substrate solubilization efficiency, HTP increased the biogas yield more effectively than mechanical pretreatment. Additionally, HTP improved the substrate’s physicochemical properties and increased the reactive surface area for microorganisms by changing the substrate morphology. Further, the biodegradability of the hydrothermally pretreated SMS was higher (87.46%) than that of the mechanically pretreated SMS (61.37%). Thus, SMS could be employed in biogas production and HTP play a key role in improving the biogas yield during SMS processing.