A review on recent advances in hydrogen energy, fuel cell, biofuel and fuel refining via ultrasound process intensification

A comprehensive review of production, applications, and the path to a sustainable energy future with hydrogen

Green hydrogen, a versatile and sustainable energy carrier, has garnered increasing attention as a critical element in the global transition to a low-carbon economy. This review article comprehensively examines the production, applications, and potential of green hydrogen, accompanied by the challenges and future prospects associated with its widespread adoption. The production of green hydrogen is a central focus, due to its environmental benefits and distinctive characteristics. The article delves into the various techniques and technologies employed in green hydrogen production, emphasizing the need for cost reduction and increased scale for economic viability. Focusing particularly on applications, the review discusses the diverse sectors where green hydrogen demonstrates immense promise. Challenges and limitations are explored, including the intermittent nature of renewable energy sources, high production costs, and the need for extensive hydrogen infrastructure. The article also highlights the pressing need for innovation in electrolysis technology and materials, emphasizing the potential for cost reduction and increased efficiency. As industries gradually transition to green hydrogen as a cleaner feedstock, its demand and cost-competitiveness are projected to increase. This review article thoroughly evaluates the current status of green hydrogen and provides valuable insights into its potential role in the transition to a sustainable energy system.

2D Monolayer Catalysts: Towards Efficient Water Splitting and Green Hydrogen Production

A viable alternative to non-renewable hydrocarbon fuels is hydrogen gas, created using a safe, environmentally friendly process like water splitting. An important role in water-splitting applications is played by the development of two-dimensional (2D) layered transition metal chalcogenides (TMDCs), transition metal carbides (MXenes), graphene-derived 2D layered nanomaterials, phosphorene, and hexagonal boron nitride. Advanced synthesis methods and characterization instruments enabled an effective application for improved electrocatalytic water splitting and sustainable hydrogen production. Enhancing active sites, modifying the phase and electronic structure, adding conductive elements like transition metals, forming heterostructures, altering the defect state, etc., can improve the catalytic activity of 2D stacked hybrid monolayer nanomaterials. The majority of global research and development is focused on finding safer substitutes for petrochemical fuels, and this review summarizes recent advancements in the field of 2D monolayer nanomaterials in water splitting for industrial-scale green hydrogen production and fuel cell applications.

Biomedical applications of cerium vanadate nanoparticles: a review

Cerium vanadate nanoparticles (CeVO4 NPs), which are members of the rare earth orthovanadate nanomaterial family, have generated considerable interest due to their diverse properties and prospective biomedical applications. The current study, which provides a comprehensive overview of the synthesis and characterization techniques for CeVO4 NPs, emphasizes the sonochemical method as an efficient and straightforward technique for producing CeVO4 NPs with tunable size and shape. This paper investigates the toxicity and biocompatibility of CeVO4 NPs, as well as their antioxidant and catalytic properties, which allow them to modify the redox state of biological systems and degrade organic pollutants. In addition, the most recent developments in the medicinal applications of CeVO4 NPs, such as cancer treatment, antibacterial activity, biosensing, and drug or gene delivery, are emphasized. In addition, the disadvantages of CeVO4 NPs, such as stability, aggregation, biodistribution, and biodegradation, are outlined, and several potential solutions are suggested. The research concludes with data and recommendations for developing and enhancing CeVO4 NPs in the biomedical industry.

Synthesis, catalysts and enhancement technologies of biodiesel from oil feedstock - A review

Biodiesel is considered as one of the most promising alternative fuels due to the depletion of fossil fuels and the need to cope with potential energy shortages in the future. This article provides a thorough analysis of biodiesel synthesis, covering a variety of topics including oil feedstock, synthesis methods, catalysts, and enhancement technologies. Different oil feedstock for the synthesis of biodiesel is compared in the review, including edible plant oil, non-edible plant oil, waste cooking oil, animal fat, microbial oil, and algae oil. In addition, different methods for the synthesis of biodiesel are discussed, including direct use, blending, thermal cracking, microemulsions, and transesterification processes, highlighting their respective advantages and disadvantages. Among them, the transesterification method is the most commonly used and a thorough examination is given of the benefits and drawbacks of utilizing enzymatic, heterogeneous, and homogeneous catalysts in this process. Moreover, this article provides an overview of emerging intensification technologies, such as ultrasonic and microwave-assisted, electrolysis, reactive distillation, and microreactors. The benefits and limitations of these emerging technologies are also reviewed. The contribution of this article is offering a thorough and detailed review of biodiesel production technologies, focusing mainly on recent advances in enhanced chemical reaction processes. This provides a resource for researchers to assess and compare the latest advancements in their investigations. It also opens up the potential for enhancing the value of oil feedstocks efficiently, contributing to the development of new energy sources.

Sono-processes: Emerging systems and their applicability within the (bio-)medical field

Sonochemistry, although established in various fields, is still an emerging field finding new effects of ultrasound on chemical systems and are of particular interest for the biomedical field. This interdisciplinary area of research explores the use of acoustic waves with frequencies ranging from 20 kHz to 1 MHz to induce physical and chemical changes. By subjecting liquids to ultrasonic waves, sonochemistry has demonstrated the ability to accelerate reaction rates, alter chemical reaction pathways, and change physical properties of the system while operating under mild reaction conditions. It has found its way into diverse industries including food processing, pharmaceuticals, material science, and environmental remediation. This review provides an overview of the principles, advancements, and applications of sonochemistry with a particular focus on the domain of (bio-)medicine. Despite the numerous benefits sonochemistry has to offer, most of the research in the (bio-)medical field remains in the laboratory stage. Translation of these systems into clinical practice is complex as parameters used for medical ultrasound are limited and toxic side effects must be minimized in order to meet regulatory approval. However, directing attention towards the applicability of the system in clinical practice from the early stages of research holds significant potential to further amplify the role of sonochemistry in clinical applications.

Extensive investigation of geometric effects in sonoreactors: Analysis by luminol mapping and comparison with numerical predictions

This investigation focuses on the influence of geometric factors on cavitational activity within a 20kHz sonoreactor containing water. Three vessels with different shapes were used, and the transducer immersion depth and liquid height were varied, resulting in a total of 126 experiments conducted under constant driving current. For each one, the dissipated power was quantified using calorimetry, while luminol mapping was employed to identify the shape and location of cavitation zones. The raw images of blueish light emission were transformed into false colors and corrected to compensate for refraction by the water-glass and glass-air interfaces. Additionally, all configurations were simulated using a sonoreactor model that incorporates a nonlinear propagation of acoustic waves in cavitating liquids. A systematic visual comparison between luminol maps and color-plots displaying the computed bubble collapse temperature in bubbly regions was conducted. The calorimetric power exhibited a nearly constant yield of approximately 70% across all experiments, thus validating the transducer command strategy. However, the numerical predictions consistently overestimated the electrical and calorimetric powers by a factor of roughly 2, indicating an overestimation of dissipation in the cavitating liquid model. Geometric variations revealed non-monotonic relationships between transducer immersion depth and dissipated power, emphasizing the importance of geometric effects in sonoreactor. Complex features were revealed by luminol maps, exhibiting appearance, disappearance, and merging of different luminol zones. In certain parametric regions, the luminol bright regions are reminiscent of linear eigenmodes of the water/vessel system. In the complementary parametric space, these structures either combine with, or are obliterated by typical elongated axial structures. The latter were found to coincide with an increased calorimetric power, and are conjectured to result from a strong cavitation field beneath the transducer producing acoustic streaming. Similar methods were applied to an additional set of 57 experiments conducted under constant geometry but with varying current, and suggested that the transition to elongated structures occurs above some amplitude threshold. While the model partially reproduced some experimental observations, further refinement is required to accurately account for the intricate acoustic phenomena involved.

Sonoactivated Nanomaterials: A potent armament for wastewater treatment

The world is currently facing a critical issue of water pollution, with wastewater being a major contributor. It comes from different types of pollutants, including industrial, medical, agricultural, and domestic. Effective treatment of wastewater requires efficient degradation of pollutants and carcinogens prior to discharge. Commonly used methods for wastewater treatment include filtration, adsorption, biodegradation, advanced oxidation processes, and Fenton oxidation, among others.The sonochemical effect refers to the decomposition, oxidation, reduction, and other reactions of pollutant molecules in wastewater upon ultrasound activation, achieving pollutants removal. Furthermore, the micro-flow effect generated by ultrasonic waves creates tiny bubbles and eddies. This significantly increases the contact area and exchange speed of pollutants and dissolved oxygen, thereby accelerating pollutant degradation. Currently, ultrasonic-assisted technology has emerged as a promising approach due to its strong oxidation ability, simple and cheap equipments, and minimal secondary pollution. However, the use of ultrasound in wastewater treatment has some limitations, such as high energy consumption, lengthy treatment time, limited water treatment capacity, stringent water quality requirements, and unstable treatment effects. To address these issues, the combination of enhanced ultrasound with nanotechnology is proposed and has shown great potential in wastewater treatment. Such a combination can greatly improve the efficiency of ultrasonic oxidation, resulting in an improved performance of wastewater purification. This article presents recent progress in the development of sonoactivated nanomaterials for enhanced wastewater disposal. Such nanomaterials are systematically classified and discussed. Potential challenges and future prospects of this emerging technology are also highlighted.

Utilizing an ultra-sonication process to optimize a two-step biodiesel production from Karanja oil

Currently, biodiesel is produced from non-edible oils, which have various poisonous and un-saponifiable components; therefore, it is harmful and unfit for humans. Biodiesel replaces petro-diesel fuel, which can be used as additives or substitutes for diesel engines. The novelty of the present study is to optimize the process parameters of a two-step (esterification and transesterification) process for biodiesel production using high free fatty acid (FFA) containing Karanja oil (Pongamia pinnata oil), with the ultrasound (US) process intensification (PI) technique, which is carried out for the first time. In the first step, a reduction in the initial FFA concentration of 11.06% was achieved through optimization of the esterification process using response surface methodology (RSM)-supported central composite design (CCD) method in which methanol:oil molar ratio of 6:1 and 60 °C reaction temperature kept as fixed parameter, whereas H₂SO₄ catalyst loading (0.5-1.5 w/w%) and reaction time (15-45 min.) were varied. The FFA value is reduced to 1.56% under the optimal condition (32.8 min reaction time and 1.14 w/w% of catalyst loading). The second step of optimization of the transesterification of esterified oil was performed by applying RSM supported Box-Behnken design (BBD) method with varying independent parameter ranges such as the molar ratio (A), CH₃OK catalyst loading (B), and reaction time (C) with the range of 6:1-9:1 (methanol: oil), 0.5-1.5 w/w%, and 10-30 min., respectively. A biodiesel yield of 98.16% was obtained under optimal conditions of a molar ratio of 7.6:1, catalyst loading of 0.98 w/w%, a reaction time of 20.6 min., and a reaction temperature of 60 °C (constant). Superior optimization results were observed than the conventional stirring method. The biodiesel's estimated characteristics were discovered to be within ASTM criteria and suitable for blending with diesel fuel.

A low-content CeOx dually promoted Ni3Fe@CNT electrocatalyst for overall water splitting

Rational construction of low-cost and high-performance electrocatalysts for water splitting is crucial for the advancement of renewable hydrogen fuel. Hybridizing heterojunctions or noble metals is one typical strategy used to boost the electrocatalytic performance for either the oxygen evolution reaction (OER) or hydrogen evolution reaction (HER). Here, low-content CeO_x (3.74 wt%) is introduced into Ni₃Fe nanoparticle-encapsulated carbon nanotubes (Ni₃Fe@CNTs/CeO_x), with both the OER and HER activities boosted, as a bifunctional electrocatalyst for overall water splitting. The composite is derived by pyrolyzing a mixture of melamine/ternary NiFeCe-layered double hydroxide. The composite electrocatalyst requires low overpotentials of 195 and 125 mV at 10 mA cm^-2 in 1.0 M KOH, respectively, which are superior to those of Ni₃Fe@CNTs/NF (313 and 139 mV) and CeO_x/NF (345 and 129 mV), and in particular, OER overpotentials of 320 and 370 mV at 50 and 100 mA cm^-2, respectively. Moreover, the composite-assembled electrolyzer for overall water splitting requires a current density of 10 mA cm^-2 at a decent cell voltage of 1.641 V. Furthermore, the enhancement is elucidated by the synergistic effect: the dual role of CeO_x in boosting the OER and HER, the highly conductive carbonaceous CNTs, large electrochemically active surface area and low charge-transfer resistance. The results can offer an effective route for designing and preparing low-cost and high-efficiency electrocatalysts for electrocatalytic water splitting.

Functionalized Metallic 2D Transition Metal Dichalcogenide-Based Solid-State Electrolyte for Flexible All-Solid-State Supercapacitors

Highly efficient and durable flexible solid-state supercapacitors (FSSSCs) are emerging as low-cost devices for portable and wearable electronics due to the elimination of leakage of toxic/corrosive liquid electrolytes and their capability to withstand elevated mechanical stresses. Nevertheless, the spread of FSSSCs requires the development of durable and highly conductive solid-state electrolytes, whose electrochemical characteristics must be competitive with those of traditional liquid electrolytes. Here, we propose an innovative composite solid-state electrolyte prepared by incorporating metallic two-dimensional group-5 transition metal dichalcogenides, namely, liquid-phase exfoliated functionalized niobium disulfide (f-NbS₂) nanoflakes, into a sulfonated poly(ether ether ketone) (SPEEK) polymeric matrix. The terminal sulfonate groups in f-NbS₂ nanoflakes interact with the sulfonic acid groups of SPEEK by forming a robust hydrogen bonding network. Consequently, the composite solid-state electrolyte is mechanically/dimensionally stable even at a degree of sulfonation of SPEEK as high as 70.2%. At this degree of sulfonation, the mechanical strength is 38.3 MPa, and thanks to an efficient proton transport through the Grotthuss mechanism, the proton conductivity is as high as 94.4 mS cm^-1 at room temperature. To elucidate the importance of the interaction between the electrode materials (including active materials and binders) and the solid-state electrolyte, solid-state supercapacitors were produced using SPEEK and poly(vinylidene fluoride) as proton conducting and nonconducting binders, respectively. The use of our solid-state electrolyte in combination with proton-conducting SPEEK binder and carbonaceous electrode materials (mixture of activated carbon, single/few-layer graphene, and carbon black) results in a solid-state supercapacitor with a specific capacitance of 116 F g^-1 at 0.02 A g^-1, optimal rate capability (76 F g^-1 at 10 A g^-1), and electrochemical stability during galvanostatic charge/discharge cycling and folding/bending stresses.

Enabling a high-performance saltwater Al-air battery via ultrasonically driven electrolyte flow

As an emerging battery technology, the Al-air flow battery (AAFB) exhibits high energy density due to the recycling of electrolytes, thus showing great potential as a type of clean and sustainable energy storage system. Conventionally, it employs an external mechanical pump to recycle the electrolyte. In this work, the saltwater AAFB in which the electrolyte is recycled by the ultrasonic capillary effect (rather than a mechanical pump) and the reaction chamber is agitated by ultrasonic vibration, is proposed and investigated. Our numerical simulations show that a travelling ultrasonic wave in the electrolyte flow system causes the capillary flow and agitation. The experimental results show that the percentage increase of the peak power density (relative to that with static electrolyte) can be up to about 7.5 times of that with the electrolyte flow driven by a mechanical pump, under the same electrolyte flow rate and concentration (3.3 ml min^-1 and 3 M NaCl). The optimal peak power density, which can be achieved by optimizing the reaction chamber thickness, electrolyte concentration and ultrasonic vibration velocity, is 43.88 mW cm^-2. This work illustrates that the acoustofluidic method can not only improve the discharge performance of the saltwater AAFB effectively, but also greatly decrease the energy consumption, weight and volume of the electrolyte driving unit of the AAFB. In addition, analyses based on experimental results show that the energy gain of a series/parallel battery system formed by multiple identical cells can be larger than one, if the number of cells in the system is large enough.

Enhanced Catalytic Performance of N-Doped Carbon Sphere-Supported Pd Nanoparticles by Secondary Nitrogen Source Regulation for Formic Acid Dehydrogenation

The development of catalysts with high selectivity, good catalytic activity, and excellent cycle performance is of significance for the application of formic acid (HCOOH, FA) as a hydrogen support. Herein, Pd is deposited on a series of N-doped carbons, which are prepared by cocarbonization of N-containing zeolite imidazole frameworks (ZIF-8) and other N/C sources (melamine, xylitol, urea, and glucose), for hydrogen generation from FA. The results demonstrate that the introduction of a secondary N/C source further affects the catalytic performance of Pd by adjusting the morphology, specific surface area, N content, and type of carbon. The effects of N atoms and the favorable reaction pathways of FA dehydrogenation were revealed by theoretical calculation. This work will improve the understanding of N doping on the decomposition mechanism of FA and provide a new approach for the rational design of metal-N-C materials.

Recent ultrasound advancements for the manipulation of nanobiomaterials and nanoformulations for drug delivery

Recent advances in ultrasound (US) have shown its great potential in biomedical applications as diagnostic and therapeutic tools. The coupling of US-assisted drug delivery systems with nanobiomaterials possessing tailor-made functions has been shown to remove the limitations of conventional drug delivery systems. The low-frequency US has significantly enhanced the targeted drug delivery effect and efficacy, reducing limitations posed by conventional treatments such as a limited therapeutic window. The acoustic cavitation effect induced by the US-mediated microbubbles (MBs) has been reported to replace drugs in certain acute diseases such as ischemic stroke. This review briefly discusses the US principles, with particular attention to the recent advancements in drug delivery applications. Furthermore, US-assisted drug delivery coupled with nanobiomaterials to treat different diseases (cancer, neurodegenerative disease, diabetes, thrombosis, and COVID-19) are discussed in detail. Finally, this review covers the future perspectives and challenges on the applications of US-mediated nanobiomaterials.

Hydrogen production from the catalytic dehydrogenation of dodecahydro-N-ethylcarbazole: effect of Pd precursor on the catalytic performance of Pd/C catalysts

In this paper, Pd/C catalysts are synthesized via Ar glow-discharge plasma reduction using activated carbon as the support and Pd(acac)₂, Pd(NO₃)₂, K₂PdCl₄, and H₂PdCl₄ as the Pd precursors, and their catalytic performances are investigated by hydrogen production from dodecahydro-N-ethylcarbazole (H12-NEC). Pd/C-A, prepared from Pd(acac)₂, which has the smallest palladium nanoparticles (1.7 nm), the highest dispersion (34%) and no residue of inorganic ions, exhibits the best catalytic activity with a hydrogen release of 5.28 wt.%, which is 2.2 times that of Pd/C-H. The order of the apparent activation energies of the prepared Pd/C catalysts, according to the kinetics of the H12-NEC dehydrogenation reaction, is as follows: Pd/C-A ≈ Pd/C-N < Pd/C-K < Pd/C-H. When Pd(acac)₂ with a large ligand acts as a cation Pd precursor, the effect of coulombic attraction to Pd²⁺ during the plasma reduction process makes it difficult for Pd nanoparticles (NPs) to migrate, which leads to the formation of ultrafine Pd NPs.

Enhancement of biohydrogen production rate in Rhodospirillum rubrum by a dynamic CO-feeding strategy using dark fermentation

BACKGROUND

Rhodospirillum rubrum is a purple non-sulphur bacterium that produces H₂ by photofermentation of several organic compounds or by water gas-shift reaction during CO fermentation. Successful strategies for both processes have been developed in light-dependent systems. This work explores a dark fermentation bioprocess for H₂ production from water using CO as the electron donor.

RESULTS

The study of the influence of the stirring and the initial CO partial pressure (p_CO) demonstrated that the process was inhibited at p_CO of 1.00 atm. Optimal p_CO value was established in 0.60 atm. CO dose adaptation to bacterial growth in fed-batch fermentations increased the global rate of H₂ production, yielding 27.2 mmol H₂ l^-1 h^-1 and reduced by 50% the operation time. A kinetic model was proposed to describe the evolution of the molecular species involved in gas and liquid phases in a wide range of p_CO conditions from 0.10 to 1.00 atm.

CONCLUSIONS

Dark fermentation in R. rubrum expands the ways to produce biohydrogen from CO. This work optimizes this bioprocess at lab-bioreactor scale studying the influence of the stirring speed, the initial CO partial pressure and the operation in batch and fed-batch regimes. Dynamic CO supply adapted to the biomass growth enhances the productivity reached in darkness by other strategies described in the literature, being similar to that obtained under light continuous syngas fermentations. The kinetic model proposed describes all the conditions tested.