Hydrogen production technologies - Membrane based separation, storage and challenges

A Review of the Recent Advances in Composite Membranes for Hydrogen Generation Technologies

Keeping global warming at 2 degrees and below as stated in the "Paris Climate Agreement" and minimizing emissions can only be achieved by establishing a hydrogen (H2) ecosystem. Therefore, H2 technologies stand out in terms of accomplishing zero net emissions. Although H2 is the most abundant element in the known universe, molecular H2 is very rare in nature and must be produced. In H2 production, reforming natural gas and renewable hydrogen processes using electrolyzers comes to the fore. The key to all these technologies is to enhance production speed, performance, and system lifetime. At this point, composite membranes used in both processes come to the fore. This review article summarizes composite membrane technologies used in methane, ethanol, and biomass steam reforming processes, proton exchange membranes, alkaline water electrolysis, and hybrid sulfur cycle. In addition to these common H2 production technologies at large quantities, the innovative systems developed with solar energy integration for H2 generation were linked to composite membrane utilization. This study aimed to draw attention to the importance of composite membranes in H2 production. It aims to prepare a guiding summary for those working on membranes by combining the latest and cutting-edge studies on this subject.

Computational evaluation of novel XCuH3 (X = Li, Na and K) perovskite-type hydrides for hydrogen storage applications using LDA and GGA approach

Hydrogen energy has attracted a lot of interest from researchers as a sustainable and renewable energy source, but there are some technical challenges related to its storage. Hydride materials demonstrate the ability to store hydrogen adequately and safely. In the current study, we have investigated the structural and optoelectronic properties of the XCuH3 (where X = Li, Na and K) perovskite-type hydride using LDA and GGA formalisms for hydrogen storage application. Electronic properties such as band structure, density of states reveal the metallic character of the studied XCuH3 hydrides. Various optical parameters such as the complex dielectric function, refractive index, extinction coefficient, absorption coefficient, reflectivity, optical conductivity, energy loss function, and joint density of states have been computed and compared. The gravimetric hydrogen storage capacity for LiCuH3, NaCuH3 and KCuH3 are found to be 4.11, 3.37 and 2.86 wt%, respectively. The computed values of the gravimetric ratio manifest that XCuH3 hydrides are potential candidates for hydrogen storage applications. These calculations are made for the first time for XCuH3 hydrides and will be inspirational in the future for comparison and for hydrogen storage purposes.

Bioconversion of volatile fatty acids from organic wastes to produce high-value products by photosynthetic bacteria: A review

Anaerobic fermentation of organic waste to produce volatile fatty acids (VFAs) production is a relatively mature technology. VFAs can be used as a cheap and readily available carbon source by photosynthetic bacteria (PSB) to produce high value-added products, which are widely used in various applications. To better enhance the VFAs obtained from organic wastes for PSB to produce high value-added products, a comprehensive review is needed, which is currently not available. This review systematically summarizes the current status of microbial proteins, H2, poly-β-hydroxybutyrate (PHB), coenzyme Q10 (CoQ10), and 5-aminolevulinic acid (ALA) production by PSB utilizing VFAs as a carbon resource. Meanwhile, the metabolic pathways involved in the H2, PHB, CoQ10, and 5-ALA production by PSB were deeply explored. In addition, a systematic resource utilization pathway for PSB utilizing VFAs from anaerobic fermentation of organic wastes to produce high value-added products was proposed. Finally, the current challenges and priorities for future research were presented, such as the screening of efficient PSB strains, conducting large-scale experiments, high-value product separation, recovery, and purification, and the mining of metabolic pathways for the VFA utilization to generate high value-added products by PSB.

Improved solar-driven water purification using an eco-friendly and cost-effective aerogel-based interfacial evaporator with exceptional photocatalytic capabilities

As a promising solution to address the global challenge of freshwater scarcity, solar-powered interfacial steam generation has undergone notable advancements. This study introduces a novel solar-driven interfacial evaporation membrane (ZnIn2S4@SiO2/ACSA, ZSAS) comprising a ZnIn2S4@SiO2 composite and a black sodium alginate aerogel infused with activated carbon. The ZSAS membrane demonstrates exceptional light absorption and thermal insulation, leading to elevated surface temperatures and reduced heat dissipation into the bulk water. Furthermore, the incorporation of AC reinforces the mechanical properties of the ZSAS membrane and enhances the water purification performance. These collective features result in an impressive evaporation rate of 1.485 kg m-2 h-1 and a high photothermal conversion efficiency of 91.2% under 1 sun irradiation for the optimal ZSAS membrane. Moreover, the optimal ZSAS membrane can effectively remove salts, heavy metal ions, and organic pollutants, benefitting from its superior evaporation separation effect and the photocatalytic properties of the ZnIn2S4@SiO2 composite.

Unleashing the power of solar light: WO3 nanorods decorated onto BiVO4 dendrites for tetracycline detoxification and water splitting

The coupling of different oxide materials in a nanohybrid enables the customization of their optical and charge transport properties, leading to improved interfacial charge segregation and migration. In this study, BiVO4/WO3 (BVW), a sunlight-driven photocatalyst with distinct mole ratios was synthesized via a facile hydrothermal approach. The resultant catalyst exhibits a nanorods shape morphology decorated onto dendrite-like matrix and is studied for photocatalytic elimination of tetracycline (TC) and photoelectrocatalytic (PEC) H2 production. The effect of illumination time, solution pH, photocatalyst concentration, and mole ratios of BiVO4 to WO3 on the photocatalytic abatement of TC were tested sequentially as effective operating factors. Under optimal condition, 3:1 BiVO4:WO3 (31BVW) nanohybrid demonstrated a maximum degradation efficacy of 96.2% (rate constant ~0.0241 min-1), which is much better than its individual components and commercial TiO2-P25 (50.9%). The resultant by-products of TC decomposition were analyzed using GC-MS to explain the degradation mechanism. Moreover, as a photoanode, 31BVW showed a high photocurrent density of 0.64 mA/cm2 at 1.23 V vs RHE and a steady photocurrent for ~6 h under chronoamperometry study at1.23 V vs RHE. However, bare BiVO4 and WO3 exhibited the photocurrent density of 0.001 mA/cm2, and 0.015 mA/cm2, respectively at 1.23 V vs RHE. The Mott-Schottky analysis of 31BVW confirms their n-type behavior, with a calculated flat band potential of -0.067 V. The hydrogen production rate was theoretically calculated as 4.56 mmolcm-2 s-1 from chronoamperometric measurements. The photocatalyst's efficacy in TC degradation was further established via its reusability upto 7 cycles. Post degradation characterization of catalyst confirms its stability in lieu of practical usage. Comparative studies with existing literature revealed the superiority of reported photocatalysts in both applications. Overall, the binary BVW photocatalyst shows great potential for removing detrimental contaminants as well as H2 production via PEC water splitting due to efficient charge separation, reduced recombination, high surface area, and widen absorption window of the nanohybrid.

Genetic engineering for biohydrogen production from microalgae

The development of biohydrogen as an alternative energy source has had great economic and environmental benefits. Hydrogen production from microalgae is considered a clean and sustainable energy production method that can both alleviate fuel shortages and recycle waste. Although algal hydrogen production has low energy consumption and requires only simple pretreatment, it has not been commercialized because of low product yields. To increase microalgal biohydrogen production several technologies have been developed, although they struggle with the oxygen sensitivity of the hydrogenases responsible for hydrogen production and the complexity of the metabolic network. In this review, several genetic and metabolic engineering studies on enhancing microalgal biohydrogen production are discussed, and the economic feasibility and future direction of microalgal biohydrogen commercialization are also proposed.

Food Waste Utilization for Reducing Carbon Footprints towards Sustainable and Cleaner Environment: A Review

There is world-wide generation of food waste daily in significant amounts, leading to depletion of natural resources and deteriorating air quality. One-third of global food produced is wasted laterally with the food value chain. Carbon footprint is an efficient way of communicating the issues related to climate change and the necessity of changing behavior. Valorization or utilization of food wastes helps in resolving issues related to environment pollution. Reduction in the carbon footprint throughout the chain of food supply makes the whole process eco-friendly. Prevailing food waste disposal systems focus on their economic and environmental viability and are putting efforts into using food waste as a resource input to agriculture. Effective and advanced waste management systems are adopted to deal with massive waste production so as to fill the gap between the production and management of waste disposal. Food waste biorefineries are a sustainable, eco-friendly, and cost-effective approach for the production of platform chemicals, biofuels, and other bio-based materials. These materials not only provide sustainable resources for producing various chemicals and materials but have the potential to reduce this huge environmental burden significantly. In this regard, technological advancement has occurred in past few years that has proven suitable for tackling this problem.

Stability Tests on Anion Exchange Membrane Water Electrolyzer under On-Off Cycling with Continuous Solution Feeding

In this study, the stability of an anion exchange membrane water electrolyzer (AEMWE) cell was evaluated in an on-off cycling operation with respect to an applied electric bias, i.e., a current density of 500 mA cm−2, and an open circuit. The ohmic and polarization resistances of the system were monitored during operation (~800 h) using electrochemical impedance spectra. Specific consideration was given to the ohmic resistance of the cell, especially that of the membrane under on-off cycling conditions, by consistently feeding the cell with KOH solution. Owing to an excess feed solution, a momentary increase in the polarization resistance was observed immediately after the open-circuit. The excess feed solution was mostly recovered by subjecting the cell to the applied electric bias. Stability tests on the AEMWE cell under on-off cycling with continuous feeding even under an open circuit can guarantee long-term stability by avoiding an irreversible increase in ohmic and polarization resistances.

Efficient removal of heavy metal ions from aqueous media by unmodified and modified nanodiamonds

This article deals with the adsorption performances of the unmodified nanodiamond (ND) and thermally oxidized nanodiamond (Ox-ND) for the removal of different heavy metal ions such as Fe (III), Cu (II), Cr (VI), and Cd (II) from wastewater. The adsorption capacities of the ions onto adsorbents are higher and follow the order: Ox-ND-3 > Ox-ND-1.5 > ND, which is consistent with their surface areas, zeta potentials, and the presence of carboxyl groups, suggesting that electrostatic attractions between the positive metal ions and the negatively charged adsorbents are the predominant adsorption mechanisms. Adsorption capacities of these adsorbents were found to be 26.8, 31.3, and 45.7 mg/g for Fe (III), 25.2, 30.5, and 44.5 mg/g for Cu (II), 33.6, 44.1, and 55.9 mg/g for Cr (VI), and 40.9, 52.9, and 67.9 mg/g for Cd (II) over ND, Ox-ND-1.5, and Ox-ND-3, respectively. The impact of various operating parameters such as agitation time, initial metal ion concentration, temperature, pH solution, adsorbent dosage, and coexistence of the metal ions on the adsorption performance of Ox-ND-3 towards Cd (II) ions along with the batch adsorption experiments were performed. The equilibrium was reached in 120 min and adsorption data were fitted well with the pseudo-second-order kinetic as well as the Freundlich isotherm models. Adsorption process was spontaneous and exothermic, while the maximum removal efficiency of Cd (II) ions occurred at pH of 6.9 and at 4 g/L dosage. These findings demonstrated that thermally oxidized nanodiamond (Ox-ND) can be a versatile adsorbent to remove the Cd (II) ions from wastewater.

Dual-Phase Mixed Protonic-Electronic Conducting Hydrogen Separation Membranes: A Review

Owing to the excellent properties of high selectivity, high thermal stability, and low cost, in the past twenty years, mixed protonic-electronic conducting hydrogen separation membranes have received extensive attention. In particular, dual-phase mixed protonic-electronic conducting membranes with high ambipolar conductivity are more attractive because of the high hydrogen permeability. This paper aimed to present a review of research activities on the dual-phase membranes, in which the components, the characteristics, and the performances of different dual-phase membranes are introduced. The key issues that affect the membrane performance such as the elimination of the inter-phase reaction, the combination mode of the phases, the phase ratio, and the membrane configuration were discussed. The current problems and future trends were simply recommended.

Zirconia-Doped Methylated Silica Membranes via Sol-Gel Process: Microstructure and Hydrogen Permselectivity

In order to obtain a steam-stable hydrogen permselectivity membrane, with tetraethylorthosilicate (TEOS) as the silicon source, zirconium nitrate pentahydrate (Zr(NO₃)₄·5H₂O) as the zirconium source, and methyltriethoxysilane (MTES) as the hydrophobic modifier, the methyl-modified ZrO₂-SiO₂ (ZrO₂-MSiO₂) membranes were prepared via the sol-gel method. The microstructure and gas permeance of the ZrO₂-MSiO₂ membranes were studied. The physical-chemical properties of the membranes were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscope (SEM), and N₂ adsorption–desorption analysis. The hydrogen permselectivity of ZrO₂-MSiO₂ membranes was evaluated with Zr content, temperature, pressure difference, drying control chemical additive (glycerol) content, and hydrothermal stability as the inferred factors. XRD and pore structure analysis revealed that, as n_Zr increased, the MSiO₂ peak gradually shifted to a higher 2θ value, and the intensity gradually decreased. The study found that the permeation mechanism of H₂ and other gases is mainly based on the activation–diffusion mechanism. The separation of H₂ is facilitated by an increase in temperature. The ZrO₂-MSiO₂ membrane with n_Zr = 0.15 has a better pore structure and a suitable ratio of micropores to mesopores, which improved the gas permselectivities. At 200 °C, the H₂ permeance of MSiO₂ and ZrO₂-MSiO₂ membranes was 3.66 × 10⁻⁶ and 6.46 × 10⁻⁶ mol·m⁻²·s⁻¹·Pa⁻¹, respectively. Compared with the MSiO₂ membrane, the H₂/CO₂ and H₂/N₂ permselectivities of the ZrO₂-MSiO₂ membrane were improved by 79.18% and 26.75%, respectively. The added amount of glycerol as the drying control chemical additive increased from 20% to 30%, the permeance of H₂ decreased by 11.55%, and the permselectivities of H₂/CO₂ and H₂/N₂ rose by 2.14% and 0.28%, respectively. The final results demonstrate that the ZrO₂-MSiO₂ membrane possesses excellent hydrothermal stability and regeneration capability.

BioH2 from Dark Fermentation of OFMSW: Effect of the Hydraulic Retention Time and Organic Loading Rate

Food wastes represent one third of all food produced worldwide. It is crucial to both prevent the production of food waste and recover the wasted fraction with the aim to valorizing it. In this context, the conversion of the organic fraction of municipal solid wastes (OFMSW) into bioH2 by dark fermentation (DF) is an important technology to valorize these wastes into renewable fuel. Nevertheless, the DF of OFMSW needs to be optimized for critical operational parameters. The main purposes of this study were to investigate (i) the effect of HRT during continuous bioH2 production through DF and (ii) the effect of organic loading rate (OLR) ruled by HRT. In this work, three HRTs (4, 5, and 6 d) were tested in a mesophilic continuous stirred-tank reactor (CSTR). The HRTs of 4, 5, and 6 days, corresponding to OLRs of 23.6, 18.0, and 10.6 g volatile solids (VS)·L−1·d−1, respectively, showed bioH2 yields of 8.48, 18.2, and 1.64 L·kg−1 VSinfluent with an H2 content of approximately 25, 32, and 5% v/v, respectively. An accumulation of volatile fatty acids (VFAs) was registered with the decrease in HRT, causing a decrease in bioH2 production. The 5 d HRT was the most favorable condition.

A Review on Advanced Manufacturing for Hydrogen Storage Applications

Hydrogen is a notoriously difficult substance to store yet has endless energy applications. Thus, the study of long-term hydrogen storage, and high-pressure bulk hydrogen storage have been the subject of much research in the last several years. To create a research path forward, it is important to know what research has already been done, and what is already known about hydrogen storage. In this review, several approaches to hydrogen storage are addressed, including high-pressure storage, cryogenic liquid hydrogen storage, and metal hydride absorption. Challenges and advantages are offered based on reported research findings. Since the project looks closely at advanced manufacturing, techniques for the same are outlined as well. There are seven main categories into which most rapid prototyping styles fall. Each is briefly explained and illustrated as well as some generally accepted advantages and drawbacks to each style. An overview of hydrogen adsorption on metal hydrides, carbon fibers, and carbon nanotubes are presented. The hydrogen storage capacities of these materials are discussed as well as the differing conditions in which the adsorption was performed under. Concepts regarding storage shape and materials accompanied by smaller-scale advanced manufacturing options for hydrogen storage are also presented.