Wood-Structured Nanomaterials as Highly Efficient, Self-Standing Electrocatalysts for Water Splitting.

Electrocatalytic water splitting (EWS) driven by renewable energy is widely considered an environmentally friendly and sustainable approach for generating hydrogen (H2), an ideal energy carrier for the future. However, the efficiency and economic viability of large-scale water electrolysis depend on electrocatalysts that can efficiently accelerate the electrochemical reactions taking place at the two electrodes. Wood-derived nanomaterials are well-suited for serving as EWS catalysts because of their hierarchically porous structure with high surface area and low tortuosity, compositional tunability, cost-effectiveness, and self-standing integral electrode configuration. Here, recent advancements in the design and synthesis of wood-structured nanomaterials serving as advanced electrocatalysts for water splitting are summarized. First, the design principles and corresponding strategies toward highly effective wood-structured electrocatalysts (WSECs) are emphasized. Then, a comprehensive overview of current findings on WSECs, encompassing diverse structural designs and functionalities such as supported-metal nanoparticles (NPs), single-atom catalysts (SACs), metal compounds, and heterostructured electrocatalysts based on engineered wood hosts are presented. Subsequently, the application of these WSECs in various aspects of water splitting, including the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), overall water splitting (OWS), and hybrid water electrolysis (HWE) are explored. Finally, the prospects, challenges, and opportunities associated with the broad application of WSECs are briefly discussed. This review aims to provide a comprehensive understanding of the ongoing developments in water-splitting catalysts, along with outlining design principles for the future development of WSECs.

Boosting Electrocatalytic Oxygen Evolution over Ce-Co9 S8 Core-Shell Nanoneedle Arrays by Electronic and Architectural Dual Engineering.

An dual electronic and architectural engineering strategy is a good way to rationally design earth-abundant and highly efficient electrocatalysts of the oxygen evolution reaction (OER) for sustainable hydrogen-based energy devices. Here, a Ce-doped Co9 S8 core-shell nanoneedle array (Ce-Co9 S8 @CC) supported on a carbon cloth has been designed and developed to accelerate the sluggish kinetics of the OER. Profiting from valance alternative Ce doping, a fine core-shell structure and vertically aligned nanoneedle arrayed architecture, Ce-Co9 S8 @CC integrates modulated electronic structure, highly exposed active sites, and multidimensional mass diffusion channels; together, these afford a favorable catalyzed OER. Ce-Co9 S8 @CC exhibits remarkable performance in the OER in an alkaline medium, where the overpotential requires only 242 mV to deliver a current density of 10 mA cm-2 for the OER; this is 70 mV superior to that of Ce-free Co9 S8 catalyst and other counterparts. Good stability and impressive selectivity (nearly 100 % Faradic efficiency) are also demonstrated. When integrated into a two-electrode OER//HER electrolyzer, the as-prepared Ce-Co9 S8 @CC displays a low operation potential of 1.54 V at 10 mA cm-2 and long-term stability, thus demonstrating great potential for economical water electrolysis.

Atom-Ratio-Conducted Tailoring of PdAu Bimetallic Nanocrystals with Distinctive Shapes and Dimensions for Boosting the ORR Performance.

Systematically manipulating the shape, dimension, and surface structure of PdAu nanocrystals is an active subject because it offers a powerful means to regulate and investigate their structure-activity relationship. Meanwhile, it is still urgent to reduce the use of two-dimensional precious-metal-based nanomaterials. This work demonstrates that PdAu nanocrystals with a variety of shapes/dimensions, including 1D anisotropic nanowires, 2D porous nanosheets, and 3D penetrative nanoflowers, can be systematically synthesized by simply adjusting the atomic ratio or the reaction time in the same protocol. The resultant PdAu nanocrystals with distinctive shapes, but the same building blocks triumphantly avoid the effects of facet and surface properties; this represents an ideal platform for directly comparing the oxygen reduction reaction (ORR) activity. 2D porous PdAu nanosheets demonstrate superior ORR performance (Eonset = 1.040 V, E1/2 = 0.932 V) compared with other-dimension-based samples and commercial Pd black; this is attributed to the abundant surface atoms and omni-directional mass-transfer channels. This work not only paves the way for systematically measuring a series of distinctive PdAu nanocrystals as non-Pt electrocatalysts, but also sheds light on the study of structures/dimensions in tuning the catalytic properties of bimetallic nanocrystals.

One-step hydroprocessing of fatty acids into renewable aromatic hydrocarbons over Ni/HZSM-5: insights into the major reaction pathways.

For high caloricity and stability in bio-aviation fuels, a certain content of aromatic hydrocarbons (AHCs, 8-25 wt%) is crucial. Fatty acids, obtained from waste or inedible oils, are a renewable and economic feedstock for AHC production. Considerable amounts of AHCs, up to 64.61 wt%, were produced through the one-step hydroprocessing of fatty acids over Ni/HZSM-5 catalysts. Hydrogenation, hydrocracking, and aromatization constituted the principal AHC formation processes. At a lower temperature, fatty acids were first hydrosaturated and then hydrodeoxygenated at metal sites to form long-chain hydrocarbons. Alternatively, the unsaturated fatty acids could be directly deoxygenated at acid sites without first being saturated. The long-chain hydrocarbons were cracked into gases such as ethane, propane, and C6-C8 olefins over the catalysts' Brønsted acid sites; these underwent Diels-Alder reactions on the catalysts' Lewis acid sites to form AHCs. C6-C8 olefins were determined as critical intermediates for AHC formation. As the Ni content in the catalyst increased, the Brønsted-acid site density was reduced due to coverage by the metal nanoparticles. Good performance was achieved with a loading of 10 wt% Ni, where the Ni nanoparticles exhibited a polyhedral morphology which exposed more active sites for aromatization.

Cellulose-based carbon nanotubes array with lawn-like 3D architecture for oxygen reduction reaction.

The conversion of biomass into high-performance carbon-based materials provides an opportunity to valorize biomass for advanced applications. Achieving this necessitates requires dedicated efforts and innovations in biocarbon synthesis, design, and applications. This study proposes the controllable conversion of biomass-derived cellulose into well-distributed carbon nanotubes (CNTs) by tuning the precipitation of cellulose pyrolysis generated vapors with in-situ formed ferric metal nanoparticles. The obtained CNTs exhibited lawn-like 3D architecture with similar length, uniform alignment, and dense distribution. The combined use of ferric chloride and dicyandiamide as the reagents with a mass ration of 0.162:1.05, demonstrated optimal performance in controlling the morphology of CNTs, enhancing the graphitization, and increasing the content of graphitic-N and pyridine-N. This multi-dimensional modification enhanced the electrocatalytic performance of the obtained CNTs, achieving an onset potential of 0.875 V vs. relative hydrogen electrode (RHE), a half-wave potential of 0.703 V vs. RHE, and a current density of -4.95 mA cm-2 during the oxygen reduction reaction. Following microbial fuel cells (MFCs) tests achieved an output voltage of 0.537 V and an output power density of 412.85 mW m-2, comparable to MFC with Pt/C as the cathode catalyst. This biomass-derived catalyst is recommended as a high-quality, non-noble metal alternative to traditional noble-metal catalysts.

Factors affecting the performance of a single-chamber microbial fuel cell-type biological oxygen demand sensor.

Microbial fuel cells (MFCs) are devices that exploit microorganisms as biocatalysts to degrade organic matter or sludge present in wastewater (WW), and thereby generate electricity. We developed a simple, low-cost single-chamber microbial fuel cell (SCMFC)-type biochemical oxygen demand (BOD) sensor using carbon felt (anode) and activated sludge, and demonstrated its feasibility in the construction of a real-time BOD measurement system. Further, the effects of anodic pH and organic concentration on SCMFC performance were examined, and the correlation between BOD concentration and its response time was analyzed. Our results demonstrated that the SCMFC exhibited a stable voltage after 132 min following the addition of synthetic WW (BOD concentration: 200 mg/L). Notably, the response signal increased with an increase in BOD concentration (range: 5-200 mg/L) and was found to be directly proportional to the substrate concentration. However, at higher BOD concentrations (>120 mg/L) the response signal remained unaltered. Furthermore, we optimized the SCMFC using synthetic WW, and tested it with real WW. Upon feeding real WW, the BOD values exhibited a standard deviation from 2.08 to 8.3% when compared to the standard BOD5 method, thus demonstrating the practical applicability of the developed system to real treatment effluents.

Optimization of integrated anaerobic digestion and pyrolysis for biogas, biochar and bio-oil production from the perspective of energy flow.

Valorization of lignocellulosic biomass via anaerobic digestion (AD) is limited by its reluctant structure, leading to a substantial energy remaining in the solid digestate. To mitigate this effect, the integration of AD and pyrolysis has attracted attention in recent years. However, the energy recovery efficiency of this cascading system is still unclear, especially the time node. Herein, a comprehensive evaluation of this integration, using varied AD periods, was conducted, to produce biogas, bio-oil and biochar, and to enhance the energy recovery, from the perspective of energy flow. The result indicated that the accumulative CH4 yields increased from 33.23 to 249.20 mL/g VS as the AD time increased from 3 to 15 days. Pyrolysis of the obtained solid digestate obtained biochar from 28.81 to 35.96 %, while the bio-oil and pyrolysis gas slowly decreased. The highest energy efficiency of 71.9 % with a net energy gain of 2.0 MJ/kg wet biomass was achieved by the coupled system optimization at an AD time of 12 days as suggested by the energy flow analysis. This study provides new insight for the maximal conversion of biomass waste into energy products and provides a new way of recycling it.

Electron transmission matrix and anion regulation strategy-derived oxygen-deficient δ-MnO2 for a high-rate and long-life aqueous zinc-ion battery.

Ion migration and electron transmission are vital for manganese dioxides in zinc ion batteries. δ-MnO2 is believed to be more suitable for zinc ion storage due to its layered structure. However, the performance of δ-MnO2 is still hampered by the frustrating conductivity and sluggish reaction kinetics. Herein, atomic engineering is adopted to modify δ-MnO2 at the atomic level to obtain oxygen-deficient δ-MnO2 (N-MnO2). Meanwhile, hollow carbon microtubes (HCMTs) obtained from green and renewable energy grass are proposed as cross-connected electron transmission matrices (CETMs) for MnO2. The biomass-derived CETMs not only optimize reaction kinetics but also facilitate the ion storage performance of MnO2. The as-prepared N-MnO2@HCMTs exhibit high rate capability and enhanced pseudocapacitve behavior contributed by the oxygen-deficient N-MnO2 and CETMs. Ex situ analysis reveals the reversible insertion/extraction of H+ and Zn2+ in N-MnO2@HCMTs during charge/discharge processes. Moreover, the quasi-solid-state N-MnO2@HCMTs//Zn cells are assembled and they deliver extraordinary discharge capacity and a long cyclic lifespan. This study may provide insights for further exploration of cathode materials in AZIBs and promote the large-scale production of aqueous Zn-MnO2 batteries.

Self­nitrogen-doped carbon materials derived from microalgae by lipid extraction pretreatment: Highly efficient catalyst for the oxygen reduction reaction.

Biomass-based nitrogen-doped carbon-based material has gradually become a premising metal alternative catalyst for oxygen reduction reaction due to their broad resources, renewable property, and low cost. However, the efficient nitrogen doping is still restricted by their low content and poor conversion efficiency. In this study, self- nitrogen -doped biomass-based carbon materials with high content of nitrogen (27.8% pyridinic-N and 40.3% graphitic-N) and hierarchical pore structure were prepared via lipid extraction pretreatment. The obtained microalgae residue carbon (MRC) catalyst exhibits superior oxygen reduction reaction performance, in terms of more preferable electrode performance and better stability, higher power density in the microbial fuel cells system compared to that of microalgae carbon (MAC). The onset potential of the MRC is 60 mV higher than that of MAC, and the maximum power density of microbial fuel cells (MFCs) with MRC as cathode catalyst reache 412.85 mW m-2. This can be attributed to the fact of that the lipid extraction was not only beneficial to the nitrogen enhancement and oriented conversion but also be conductive to the structure construction. The synergistic effect between active sites and hierarchical structure endows the catalyst excellent ORR performance and good stability in the MFCs system.

Microwave catalytic co-pyrolysis of Chlorella vulgaris and high density polyethylene over activated carbon supported monometallic: Characteristics and bio-oil analysis.

Activated carbon (AC) has attracted much attention owing to its low cost and abundant sources. In this paper, three monometallic supported catalysts were prepared using AC as support (Ce/AC, Fe/AC, Ni/AC), and the effects of three catalysts on the microwave co-pyrolysis of Chlorella vulgaris (C. vulgaris) with high density polyethylene (HDPE) were studied. The results showed that the co-pyrolysis characteristics of C. vulgaris/HDPE = 1:1 (C1HP1) were significantly improved by three catalysts at high additions (>20 %). Among them, the C1HP1 group with 50 % Fe/AC addition had the shortest co-pyrolysis reaction time (2901 s). Besides, Ce/AC and Fe/AC have a promoting effect on bio-oil yields, while Ni/AC has an inhibiting effect. The maximum bio-oil yield (25.6 %) was obtained under 40 % addition of Fe/AC. Moreover, Ce/AC obtained the highest hydrocarbons content (66.68 %), while Fe/AC obtained the highest aromatic hydrocarbons content (36.64 %). Additionally, Ce/AC had the highest deoxygenation efficiency (47.33 %) and denitrification efficiency (42.28 %).

Effect of functional group and structure on hydrophobic properties of environment-friendly lignin-based composite coatings.

Hydrophobic coatings are widely used in a variety of materials surfaces. However, it remains a great challenge for the non-toxic and environmentally-friendly production of hydrophobic coatings. Herein, two nano-scale spherical lignin/SiO2 composite particles are synthesized based on the electrostatic interaction and the steric hindrance effect inspired by the self-protection of straw. Introduction of positively charged quaternary ammonium enhances the possibility of electrostatic self-assembly between lignin and SiO2 for QAL/SiO2, and access of super-long hydrophobic chains induces the formation of nano-sized particles for QALC12/SiO2. The coatings were fabricated by simply spraying on substrates and hydrophilic/hydrophobic properties were detected. The results show that the long hydrophobic chain can enhance the hydrophobic properties of lignin polymers (CA = 129°) and the spherical micro-nano structure is beneficial to improve the hydrophobic properties of the lignin/SiO2 composite (CA = 137°). Meanwhile, the hydrophobic coating has good self-cleaning performance. The excellent hydrophobic and self-cleaning properties are mainly benefited from the nano effect, reasonable hydrophilic/hydrophobic structure, and good dispersibility of spherical structure. This work not only provides a kind of lignin-based nano-scale waterproof coatings holding excellent properties in terms of cost, scalability, and robustness, but also has important significance for the high-value utilization of biomass resources.

A critical review on retaining antibiotics in liquid digestate: Potential risk and removal technologies.

Substantial levels of antibiotics remain in liquid digestate, posing a significant threat to human safety and the environment. A comprehensive assessment of residual antibiotics in liquid digestate and related removal technologies is required. To this end, this review first evaluates the potential risks of the residual antibiotics in liquid digestate by describing various anaerobic digestion processes and their half-lives in the environment. Next, emerging technologies for removing antibiotics in liquid digestate are summarized and discussed, including membrane separation, adsorption, and advanced oxidation processes. Finally, this study comprehensively and critically discusses these emerging technologies' prospects and challenges, including techno-economic feasibility and environmental impacts.

Biochemical methane potential prediction for mixed feedstocks of straw and manure in anaerobic co-digestion.

To rapidly estimate the biochemical methane potential (BMP) of feedstocks, different multivariate regression models were established between BMP and the physicochemical indexes or near-infrared spectroscopy (NIRS). Mixed fermentation feedstocks of corn stover and livestock manure were rapidly detected BMP in anaerobic co-digestion (co-AD). The results showed that the predicted accuracy of NIRS model based on characteristic wavelengths selected by multiple competitive adaptive reweighted sampling outperformed all regression models based on the physicochemical indexes. For the NIRS regression model, coefficient of determination, root mean squares error, relative root mean squares error, mean relative error and residual predictive deviation of the validation set were 0.982, 6.599, 2.713%, 2.333% and 7.605. The results reveal that the predicted accuracy of NIRS model is very high, and meet the requirements of rapid prediction of BMP for co-AD feedstocks in practical biogas engineering.

Assessment of Coproduction of Ethanol and Methane from Pennisetum purpureum: Effects of Pretreatment, Process Performance, and Mass Balance.

To overcome the structural complexity and improve the bioconversion efficiency of Pennisetum purpureum into bioethanol or/and biomethane, the effects of ensiling pretreatment, NaOH pretreatment, and their combination on digestion performance and mass flow were comparatively investigated. The coproduction of bioethanol and biomethane showed that 65.2 g of ethanol and 102.6 g of methane could be obtained from 1 kg of untreated Pennisetum purpureum, and pretreatment had significant impacts on the production; however, there is no significant difference between the results of NaOH pretreatment and ensiling-NaOH pretreatment in terms of production improvement. Among them, 1 kg of ensiling-NaOH treated Pennisetum purpureum could yield 269.4 g of ethanol and 144.5 g of methane, with a respective increase of 313.2% and 40.8% compared to that from the untreated sample; this corresponded to the final energy production of 14.5 MJ, with the energy conversion efficiency of 46.8%. In addition, for the ensiling-NaOH treated Pennisetum purpureum, the energy recovery from coproduction (process III) was 98.9% higher than that from enzymatic hydrolysis and fermentation only (process I) and 53.6% higher than that from anaerobic digestion only (process II). This indicated that coproduction of bioethanol and biomethane from Pennisetum purpureum after ensiling and NaOH pretreatment is an effective method to improve its conversion efficiency and energy output.

Encapsulation of Fe nanoparticles into an N-doped carbon nanotube/nanosheet integrated hierarchical architecture as an efficient and ultrastable electrocatalyst for the oxygen reduction reaction.

The exploration of cost-effective, highly efficient and robust electrocatalysts toward the oxygen reduction reaction (ORR) is of paramount significance for the advancement of future renewable energy conversion devices, and yet still remains a great challenge. Herein, we demonstrate a straightforward one-step pyrolysis strategy for the scalable synthesis of an iron-nitrogen-carbon hierarchically nanostructured catalyst, in which Fe-based nanoparticles are encapsulated in bamboo-like N-doped carbon nanotubes in situ rooted from porous N-doped carbon nanosheets (Fe@N-C NT/NSs). The delicate fabrication of such an 0D/1D/2D integrated hierarchical architecture with encased Fe species and open configuration renders the formed Fe@N-C NT/NSs with sufficient confined active sites, reduced charge transfer resistance, improved diffusion kinetics and outstanding mechanical strength. As such, compared with commercial Pt/C, the optimized Fe@N-C NT/NSs catalyst exhibits efficient ORR activity, superior durability and strong tolerance to methanol in KOH medium. More impressively, when assembled as a cathode catalyst in a microbial fuel cell, the Fe@N-C NT/NSs electrode displays significantly enhanced power density and output voltage in comparison with commercial Pt/C, holding great promise in practical energy conversion devices. What's more, the simple yet reliable synthesis strategy developed here may shed light on the future design of advanced high-efficiency hierarchical architectures for diverse electrochemical applications and beyond.

Nonenzymatic electrochemical detection of glucose based on palladium-single-walled carbon nanotube hybrid nanostructures.

A new electrocatalyst, palladium nanoparticle-single-walled carbon nanotube (Pd-SWNTs) hybrid nanostructure, for the nonenzymatic oxidation of glucose was developed and characterized by X-ray diffraction (XRD) and the transmission electron microscope (TEM). The hybrid nanostructures were prepared by depositing palladium nanoparticles with average diameters of 4-5 nm on the surface of single-walled carbon nanotubes (SWNTs) via chemical reduction of the precursor (Pd(2+)). The electrocatalyst showed good electrocatalytic activity toward the oxidation of glucose in the neutral phosphate buffer solution (PBS, pH 7.4) even in the presence of a high concentration of chloride ions. A nonenzymatic amperometric glucose sensor was developed with the use of the Pd-SWNT nanostructure as an electrocatalyst. The sensor had good electrocatalytic activity toward oxidation of glucose and exhibited a rapid response (ca.3 s), a low detection limit (0.2 +/- 0.05 microM), a wide and useful linear range (0.5-17 mM), and high sensitivity (approximately 160 microA mM(-1) cm(-2)) as well as good stability and repeatability. In addition, the common interfering species, such as ascorbic acid, uric acid, 4-acetamidophenol, 3,4-dihydroxyphenylacetic acid, and so forth did not cause any interference due to the use of a low detection potential (-0.35 V vs SCE). The sensor can also be used for quantification of the concentration of glucose in real clinical samples. Therefore, this work has demonstrated a simple and effective sensing platform for nonenzymatic detection of glucose.

Bioaugmentation for overloaded anaerobic digestion recovery with acid-tolerant methanogenic enrichment.

This study aims to investigate the performance of bioaugmentation with an acid-tolerant methanogenic culture to recover deteriorated anaerobic digestion caused by organic overloading. The function of bioaugmentation was evaluated in terms of substance metabolism, microbial community structure, and gene function. Our findings demonstrate that routine bioaugmentation effectively recovered the failing digester by degrading accumulated volatile fatty acids and increasing pH. In contrast, a non-bioaugmentation reactor (control) did not recover by itself, while abiotic augmentation restored the digestion performance temporarily but the digester failed again at an organic loading rate of 1.5 g L-1 d-1. Using whole genome pyrosequencing analysis, we found that after bioaugmentation, the populations of Methanothrix (acetoclastic methanogens) and Methanolinea (hydrogenotrophic methanogens) increased significantly, which may be the main contributors for the positive effect on methane production. On the genic level, bioaugmentation may enhance the function of genes involved in cell motility, signal transduction mechanisms for methanogens, and energy production and conversion for bacteria.

Hydrolysis dynamics for batch anaerobic digestion of elephant grass.

Elephant grass might be a potential source of fine chemical precursors and bioenergy. In the present study, we investigated the dynamics of hydrolysis of elephant grass. Three models were used to fit the hydrolysis rate constants-flat, spherical, and cylindrical models. The hydrolysis rate constants obtained using the spherical model presented the best fit between the experimental and theoretical values. Furthermore, we determined the secondary reinforcement points and interventions that can be introduced to speed up the hydrolysis process. Our findings will provide information for studies on the hydrolysis of elephant grass and promote its application in the biogas industry as an alternative biofuel.

Vertical distribution of microbial community and metabolic pathway in a methanogenic propionate degradation bioreactor.

The methanogenic propionate degradation consortia were enriched in a propionate-fed semi-continuous bioreactor. The microbial community shift with depth, the microbial network and its correlation with metabolic pathway were also investigated. The results demonstrated that the maximum organic loading rate (OLR) of the reactor was 2.5g propionic acid (HPr) L-1d-1 with approximately 1.20LL-1d-1 of volumetric methane production (VMP). The organisms in the enrichment were spanning 36 bacterial phyla and 7 archaeal orders. Syntrophobacter, the main Hpr oxidizer in the digester, dominated bacteria with relative abundance changing from 63% to 37% with depth. The predominant methanogens shift from hydrogenotrophic Methanoculleus (∼60%) at the upper liquid layer to acetoclastic Methanothrix (∼51%) at the lower sediment layer in the bioreactor. These methanogens syntrophically support Syntrophobacter by degrading HPr catabolism by-products (H2 and acetate). Other bacteria could scavenge anabolic products (carbohydrate and protein) presumably derived from detrital biomass produced by the HPr-degrading community.