Lignin, a complex phenolic polymer abundantly present in the papermaking and biofuel industries, stands out as a cost-effective, plentiful, and non-toxic material. In recent years, there has been significant interest in utilizing this green biopolymer for energy storage devices. This review thoroughly examines lignin structure, chemistry, and classification based on separation techniques. It then explores the most recent breakthroughs in creating carbon materials (nanosheets, nanofibers, spheres, composites, and 3D hierarchical porous carbon) from lignin, discussing its versatility in supercapacitors and batteries. Finally, this study highlights future materials and their prospects, the critical challenges which must be addressed while suggesting future research avenues for lignin-derived carbon materials in energy storage. By combining insights from different studies, this review aims to offer readers a thorough understanding of how lignin-derived carbon materials could play a crucial role in promoting sustainable energy solutions.

Lignin, a paper and pulp industry waste product, has attracted significant attention in recent years as a promising sustainable material for high-end energy applications. Herein, we examine lignin as a potential material for ionic thermoelectric hydrogels and carbon-based materials. Optimized lignin-derived hydrogels demonstrate a remarkable Seebeck coefficient of 3.63 mV/K when subjected to an axial temperature gradient. Furthermore, synthesized lignin-based porous carbon materials exhibit exceptional performance as supercapacitor electrodes, with a superior specific capacitance of 56.3 F/g at 0.5 A/g. Lignin-based hydrogels and porous carbon electrodes offer a promising path towards the development of lignin-derived ionic thermoelectric supercapacitors.

Wood-based ionic conductive membranes have emerged as a new paradigm for low-grade thermal energy harvesting applications due to their unique andtailorable structures. Herein, a lignin-derivedionic conducting membrane with hierarchical aligned channels is synthesized viaa double network crosslinking approach. Their excellent thermal stability andsuperior swelling ratio allow their optimization as low-grade heat recovery technologies. Several vertically aligned nanoscaleconfinements are found in the synthesized membranes, contributing towardenhanced ionic diffusion. Among all the combinations, the membrane comprising69.2 wt.% of lignin and infiltrated with 0.5 m KOH exhibits anexceptional ionic figure of merit (ZTi) of 0.25, relatively higher ionic conductivity(51.5 mS cm-1), lower thermal conductivity(0.195 W m-1 center dot K), and a remarkable ionic Seebeck coefficientof 5.71 mV K-1 under the application of an axialtemperature gradient. A numerical model is also utilized to evaluate theveracity of experimental observations and to gain a better understanding of thefundamental mechanisms involved in attaining such values. These results displaythe potential of lignin-basedmembranes for future thermal energy harvesting applications and are a new facetin thermoelectric energy conversion which is certain to pave the way forfurther investigations on sustainable ionic conductive membranes. Lignin-based ionic thermoelectric membranes with hierarchically aligned channels are synthesized for efficient low-grade thermal energy harvesting. These membranes showcase exceptional ionic conductivity, thermopower, thermal stability, and unique properties, achieving an impressive ionic figure of merit of 0.25, setting a new standard in sustainable thermoelectric energy conversion. These findings unveil promising potential for sustainable ionic conductive membranes in thermal energy harvesting.image

The use of carbon fibre (CF)-based composites is of growing global importance due to their application in high-end sectors such as aerospace, automotive, construction, sports and leisure amongst others. However, their current high production cost, high carbon footprint and reduced production capability limit their use to high-performance and luxury applications. Approximately 50% of the total cost of CF production is due to the thermal conversion of polyacrylonitrile (PAN) precursor fibre (PF) to CF as it involves the use of high energy consumption and low heating efficiency in large furnaces. Looking at this scenario, this study proposes in the present study to use microwave (MW) heating to convert PF to CF. This is scientifically and technologically challenging since PF does not absorb microwave energy. While MW plasma has been utilised to carbonise fibres, it is the high temperature from the plasma that does the carbonisation and not the MW absorption of the fibres. Therefore, for the first time, this research shows how carbonisation temperatures of >1000 °C can be reached in a matter of seconds through the use of a novel microwave (MW) susceptor nanocoating methodology developed via a layer-by-layer assembly of multiwall carbon nanotubes (MWCNTs) on the PF surface. Remarkably, these CFs can be produced in an inexpensive domestic microwave and exhibit mechanical performance equivalent to CF produced using conventional heating. Additionally, this study provides a life cycle and environmental impact analysis which shows that MW heating reduces the energy demand and environmental impact of lignin-based CF production by up to 66.8% and 69.5%, respectively. Graphical Abstract

This chapter examines the potential for nanomaterials to enhance the anaerobic digestion (AD) of biomass for bioenergy and biofuel production. The impact of nanoparticles on methanogenesis, process stability, and impurities in biogas production is discussed. This chapter delves into different types of nanomaterials, including metallic, metal oxide, carbon-based, and multicompound nanoparticles, and their effects on the AD process. Furthermore, the factors affecting the efficacy of nanoparticles, such as size, concentration, pH, pressure, and temperature, are discussed along with the synthesis routes of nanoparticles. The study concludes with an analysis of the energy and cost implications of using nanoparticles in AD and the challenges and future prospects for their incorporation. Overall, the research highlights the use of nanomaterials in optimizing the AD process for sustainable bioenergy and biofuel production.

This work presents the first production, characterisation and life cycle analysis of composite materials produced from injection moulded polyamide reinforced with short lignin-based carbon fibre (CF). To produce these composites many challenges associated with the production of lignin CF have been resolved through the uti-lisation of thermoplastic polyurethane blend with Alcell organosolv lignin. These CFs have been utilised to reinforce polyamide 66 (PA66) and their performance as a reinforcement have been compared with a textile grade PAN CF. Composites have been prepared using short CF and injection moulding with results compared in terms of interfacial interactions, and composite mechanical performance. It was found that lignin-based CF in-creases crystallinity in the PA66. The increased matrix affinity of the lignin-based CF may be attributed to increased oxygen on the lignin CF which has been retained from the lignin precursor fibre. When considering that the lignin CF reach equivalent diameter to the PAN CF, the mechanical properties of lignin based CF are com-parable to that of PAN CF. Life cycle analysis modelling predicts that the replacement of PAN CF with lignin CF reduces the global warming potential by 54 % for these materials.

The development of next-generation sustainable energy storage devices is attracting a lot of attention. This study explores the potential use of lignin, a biopolymer typically considered a byproduct of the paper and pulp industry, as a starting material for producing hydrogels through chemical crosslinking. The resulting hydrogels are then evaluated for their efficacy as precursors for electrolyte and electrode preparation in the development of a supercapacitor. Several concentrations of lignin and crosslinker were evaluated to determine the optimal conditions for producing hydrogel electrolytes. The optimised hydrogels exhibited excellent properties, including high swelling capacity, an interconnected macroporous morphology, and structural integrity. The carbonisation of lyophilised lignin hydrogels produced lignin-derived carbon materials with tailored nanoporous honeycomb-like structures. The integration of chemically crosslinked lignin hydrogel electrolytes with lignin-derived carbon electrodes resulted in a sustainable supercapacitor with superior electrochemical properties. The resulting all-lignin-based supercapacitors demonstrated a capacitance of 40.7 F/g at 0.5 A/g current density, with a capacity retention of 60% at higher current densities. The results of this study highlight the promise of lignin-based materials as both electrodes and electrolytes for the creation of environmentally sustainable, high-performance supercapacitors.

In the pursuit of sustainable biomass utilization, this study investigates the hydrothermal treatment of birchwood and its subsequent impact on enzymatic hydrolysis lignin (EHL). Additionally, birchwood undergoes processing with NaOH (4% w/w) within a Parr reactor to precipitate lignin from the black liquor, resulting in lignin-rich substrates (LRSs) which are then subject to thorough characterization. Notably, EHL produced after hydrothermal pretreatment at 190 °C exhibits the highest lignin content at 67%, while kraft lignin (KL) obtained at 140 °C (pH 1.5) produces 65% lignin content. Among these LRSs, the KL sample produced at 190 °C (pH 4) stands out, displaying a robust aromatic skeletal structure and an abundance of methoxyl groups, primarily owing to its high purity. Furthermore, for these LRSs' it is shown that chemical configuration influences their thermal behaviour, allowing the lignin to be tailored for diverse applications, from low melting point materials to carbonaceous materials capable of withstanding temperatures exceeding 700 °C. This comprehensive understanding of the chemical, thermal, and physical attributes of LRSs not only enriches our knowledge of lignin-rich substrates but also paves the way for the development of sustainable bio-based materials, marking a step towards sustainable materials development.

Lignin-derived porous carbons have great potential for energy storage applications. However, their traditional synthesis requires highly corrosive activating agents in order to produce porous structures. In this work, an environmentally friendly and unique method has been developed for preparing lignin-based 3D spherical porous carbons (LSPCs). Dropwise injection of a lignin solution containing PVA sacrificial templates into liquid nitrogen produces tiny spheres that are lyophilized and carbonized to produce LSPCs. Most of the synthesized samples possess excellent specific surface areas (426.6-790.5 m2/g) along with hierarchical micro- and mesoporous morphologies. When tested in supercapacitor applications, LSPC-28 demonstrates a superior specific capacitance of 102.3 F/g at 0.5 A/g, excellent rate capability with 70.3% capacitance retention at 20 A/g, and a commendable energy density of 2.1 Wh/kg at 250 W/kg. These materials (LSPC-46) also show promising performance as an anode material in sodium-ion batteries with high reversible capacity (110 mAh g-1 at 100 mA g-1), high Coulombic efficiency, and excellent cycling stability. This novel and green technique is anticipated to facilitate the scalability of lignin-based porous carbons and open a range of research opportunities for energy storage applications.

Converting waste heat from solar radiation and industrial processes into useable electricity remains a challenge due to limitations of traditional thermoelectrics. Ionic thermoelectric (i-TE) materials offer a compelling alternative to traditional thermoelectrics due to their excellent ionic thermopower, low thermal conductivity, and abundant material options. This review categorizes i-TE materials into thermally diffusive and thermogalvanic types, with an emphasis on the former due to its superior thermopower. This review also highlights the i-TE materials for creating ionic thermoelectric supercapacitors (ITESCs) that can generate significantly higher voltages from low-grade heat sources compared to conventional technologies. Additionally, it explores thermogalvanic cells and combined devices, discussing key optimization parameters and theoretical modeling approaches for maximizing material and device performance. Future directions aim to enhance i-TE material performance and address low energy density challenges for flexible and wearable applications. Herein, the cutting-edge of i-TE materials are comprehensively outlined, empowering researchers to develop next-generation waste heat harvesting technologies for a more sustainable future.

Conventional fertilizers face environmental and economic challenges due to their high solubility, leading to significant losses via runoff and leachate. This study presents a biodegradable hydrogel, synthesized from lignin and polyvinyl alcohol (PVA), designed as an eco-friendly carrier for struvite (fertilizer) with controlled phosphate release. The hydrogel was analysed through scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Thermogravimetric analysis (TGA) and Differential scanning calorimetry (DSC). Furthermore, the prepared hydrogels demonstrated high water absorption capacities (963.4 %, 706.4 %, and 410 % for LH4, 4 , LH8, 8 , and LH12, 12 , respectively) and exhibited Fickian diffusion behaviour. Phosphate release studies showed a gradual release over 6-8 h with concentrations of 20.5 ppm, 19.45 ppm, and 17.85 ppm for St-LH4, 4 , St-LH8, 8 , and St-LH12. 12 . These lignin-based hydrogels offer a promising, cost-effective solution for slow-release fertilizers with high efficiency.

The efficient and economical conversion of low-grade waste heat into electricity has promising potential to combat the greenhouse effect and expedite the shift towards sustainable development. This study presents an innovative and appealing approach through the utilization of lignin, an abundant waste product derived from the paper and pulp industry, to develop hydrogels as compelling and sustainable materials for application in ionic thermoelectricity. Various compositions were evaluated to examine the impacts of varying lignin concentrations, types of electrolytes, concentrations of crosslinkers, and electrolyte concentrations on the ionic thermoelectric performance of the hydrogels. The optimized lignin-derived hydrogel, infiltrated with a 6 M KOH electrolyte, demonstrates high ionic conductivity (226.5 mS/cm) and a superior Seebeck coefficient of 13 mV/K. This results in a remarkable power factor (3831 µW/m·K 2 ) that leads to an impressive Figure of merit (ZT i ) (3.75), surpassing most of the existing state-of-the-art materials and making it the most efficient sustainable ionic thermoelectric material reported until now. These findings underscore the exceptional performance of lignin-based hydrogels in the realm of low-grade waste energy harvesting applications. The present study contributes to address the challenges posed by waste heat through effectively harnessing low-grade waste heat through the utilization of sustainable lignin-based hydrogels while reducing the reliance on fossil fuels and minimizing greenhouse gas emissions. Graphical Abstract

Clean fuels play a crucial role in the industrialized world's efforts to combat greenhouse gas emissions. Among the cleanest fuels available, hydrogen stands out as it produces water as a byproduct during combustion. To ensure the sustainable generation of clean fuels, it is imperative to produce hydrogen from environmentally friendly and renewable sources. Biological processes present a promising avenue for the production of hydrogen from affordable and sustainable bio-resources, including biomass and solar energy, using diverse techniques such as direct/indirect photolysis, photo-fermentation, dark-fermentation, and Microbial electrolysis cell. This comprehensive study delves into various aspects of biological hydrogen production, encompassing discussions on microorganisms, different types of substrates and their concentrations, the role of chemical additives, and key operational parameters like temperature, pH, agitation, and insights into hydrogenase and nitrogenase properties. For light-dependent processes, the study also explores the influence of illumination systems. Furthermore, the research examines different configurations of biological processes, integrating light, dark, and photofermentation in two- and three-component systems. By investigating these critical factors, the study aims to shed light on optimizing biological hydrogen production. The findings offer valuable insights for advancing the sustainable and efficient utilization of clean fuels in the global effort to mitigate greenhouse gas emissions.

Microbial electrolysis cell (MEC) is a fundamental type of bio-electrochemical system. MEC is a novel and emerging renewable energy technology that is based on biomass. The behavior of the MEC system is highly nonlinear due to the complexity of its dynamics. For the desired optimal production of hydrogen, feedback control of MEC processes is necessary. Due to the novelty of MEC, limited research is available on its control. Studies on linear model-based robust control of MEC processes are missing. In this article, we develop a nonlinear dynamic model for MEC, linearize this model, and calculate a linear time-invariant transfer function. Based on this linearization, a fixed-structure, optimal and robust controller is proposed to achieve a fast-settling time exhibiting no overshoot and having zero steady-state error. The robustness of the developed controller is evaluated for parameter uncertainty, measurement noise, and disturbance rejection. Batch biomass processes are fed only at the start of each process cycle. The output does not follow the desired response when the substrate or biomass is consumed. Then, the error accumulates, and it causes the control effort to increase unboundedly. The existing literature on control of fed-batch MEC processes does not consider this integral windup phenomenon. In this article, we also develop an anti-windup control strategy to eliminate the integral windup error and to avoid any possible instability or destruction. The overall conclusion of our study is that the developed robust controller achieves a faster and more robust response than the existing controllers. We provide an anti-integral windup solution to eliminate windup errors in feedback control of fed-batch MEC processes.

BACKGROUND: The increase in energy and water demand due to industrialization and urbanization requires prioritized solutions for a sustainable future. Microbial electrolysis cells (MECs) have shown huge potential for biohydrogen production along with wastewater treatment. This study examined the effectiveness of employing nickel foam as an anode material for biohydrogen production from the widely available potato industry effluent. RESULTS: Hydrogen production rate increases exponentially with the increase in applied voltage. A maximum hydrogen production rate of 0.69 +/- 0.02 m(3) H-2 m(-3) reactor volume d(-1) was achieved at 0.9 V with a maximum chemical oxygen demand removal efficiency of 97% at 0.8 V. The effluent of the 0.8 V cycle had the least salinity, low total dissolved solids, 84% reduced total hardness, highest effluent clarity (4.30 NTU, and negligible quantity of heavy metals. CONCLUSION: This study successfully produced biohydrogen from potato wastewater within 5 days of operation along with wastewater treatment of the substrate. The improved performance of the system can be attributed to the unique characteristics of nickel foam, such as high porosity, large surface area and excellent conductivity. The findings of this study have implications for the sustainable treatment of domestic and agro-industrial wastewater and the development of efficient and low-cost bioelectrochemical systems for renewable energy production. (C) 2023 Society of Chemical Industry (SCI).

The world is facing a serious energy crisis and environmental pollution problems due to a sharp increase in the world population. Bioenergy is an eminent solution to these problems. Anaerobic digestion is a green energy technology used worldwide for the conversion of organic waste to biogas. It is reported that organic wastes are hard to digest and need some technical improvement in the anaerobic digestion process to improve biogas yield. Iron-based additives, due to their electron acceptance and donation capabilities, have been emphasized as being exceptional in improving anaerobic digestion process efficiency amongst all other enhancement options. This study reviews the major available types of iron-based additives, their characteristics, and their preparation methods. The preferred iron-based additive that has a significant effect on the enhancement of biogas yield is also discussed. The use of iron-based additives in the anaerobic digestion process with varying dosages and their impact on the biogas generation rate is also being studied. Substrates, operating parameters, and types of anaerobic digesters used in recent studies while researching the effects of iron-based additives are also part of this review. Lastly, this study also confirms that iron-based additives have a significant effect on the reduction rate of the volatile suspended solids, methane content, biogas yield, and volatile fatty acids.

Lignin in advanced energy applications: source, extraction methodolgy, structure/property relationships.

Cellulose, an abundant natural polymer, has promising potential to be used for energy storage systems because of its excellent mechanical, structural, and physical characteristics. This review discusses the structural features of cellulose and describes its potential application as an electrode, separator, and binder, in various types of high-performing batteries. Various surface and structural characteristics of cellulose (e.g., fiber size, surface functional groups, the hierarchy of pores, and porosity levels) that contribute to its electrochemical performance are discussed. Cellulose structure/property/processing/function relationships are further focused and elucidated in terms of the latest developments in the emerging field of sustainable materials in Li-Ion, Na-Ion, and LiS batteries.

Sustainable materials are attracting a lot of attention since they will be critical in the creation of the next generation of products and devices. In this study, hydrogels were effectively synthesized utilizing lignin, a non -valorised biopolymer from the paper industry. This study proposes a method based on utilizing lignin to create highly swollen hydrogels using poly(ethylene) glycol diglycidyl ether (PEGDGE) as a crosslinking agent. The influence of different crosslinker ratios on the structural and chemical properties of the resultant hydrogels was investigated. Pore size was observed to be lowered when the amount of crosslinker was increased. The inclusion of additional hydrophilic groups in the hydrogel network decreased the swelling capacity of the hydrogels as the crosslinking density increases. These precursor materials were carbonised and electrochemically tested for application as electrodes for supercapacitors with capacitance characterized as a function of crosslinker ratio.