Search Results (19)

Green hydrogen production from water electrolysis (WE) is one of the most promising technologies to realize a decarbonized future and efficiently utilize intermittent renewable energy. Among the various WE technologies, the emerging anion exchange membrane (AEMWE) technology shows the greatest potential for producing green hydrogen at a competitive price. To achieve this goal, simple methods for the large-scale synthesis of efficient and low-cost electrocatalysts are needed. This paper proposes a very simple and scalable process for the synthesis of nanostructured NiCo- and NiFe-based electrode materials for a zero-gap AEMWE full cell. For the preparation of the cell anode, oxides with different Ni molar fractions (0.50 or 0.85) are synthesized by the sol–gel method, followed by calcination in air at different temperatures (400 or 800 °C). To fabricate the cell cathode, the oxides are reduced in a H₂/Ar atmosphere. Electrochemical testing reveals that phase purity and average crystal size significantly influence cell performance. Highly pure and finely grained electrocatalysts yield higher current densities at lower overpotentials. The best performing membrane electrode assembly exhibits a current density of 1 A cm⁻² at 2.15 V during a steady-state 150 h long stability test with 1 M KOH recirculating through the cell, the lowest series resistance at any cell potential (1.8 or 2.0 V), and the highest current density at the cut-off voltage (2.2 V) both at the beginning (1 A cm⁻²) and end of tests (1.78 A cm⁻²). The presented results pave the way to obtain, via simple and scalable techniques, cost-effective catalysts for the production of green hydrogen aimed at a wider market penetration by AEMWE. Full article

In view of achieving decarbonization targets, green hydrogen has emerged as a promising low-emission alternative. Typically, green hydrogen is produced by splitting water using various electrolysis technologies powered by renewable energy. Among these, alkaline electrolyzers have been proven as suitable for large-scale applications, operating effectively in alkaline environments under near-atmospheric pressure levels and temperatures. Once produced, H₂ must undergo purification for use in industrial and mobility sectors, with particularly stringent purification requirements for fuel applications. Despite the relevance of H₂ purification due to its usage as an energy carrier, no comprehensive analyses of H₂ purification trains downstream of H₂ production are available in the literature. To fill this gap, the aim of this work is to perform a detailed technical assessment of purification trains downstream of alkaline water electrolyzers, considering KOH removal, oxygen removal, compression and dehydration. Different case studies are discussed, focusing on the alkaline electrolyzer operating pressure (i.e., atmospheric or higher) and considering the application of H₂ in both the industrial and mobility sectors. The design and methodology of the process were developed within the Aspen Plus^® simulation environment, to support the electrolyzers’ integration in industrial settings. Full article

Rare-earth molten-salt electrolysis slag contains a substantial quantity of rare-earth elements, rendering it a valuable secondary resource for rare-earth recovery. To achieve the efficient recovery of praseodymium (Pr), neodymium (Nd), lithium (Li), and fluorine (F) from rare-earth molten-salt electrolysis slag, this paper proposes an atmospheric alkaline leaching method. The leaching efficiency of Nd, Pr, F (95.02%), and Li (95.87%) can be reached at a NaOH concentration of 80%, a reaction temperature of 180 °C, a reaction time of 2 h, and an alkali to slag ratio of 3:1. Leaching efficiency kinetic analysis shows that the leaching processes of fluorine and lithium are both controlled by interfacial chemical reactions, with apparent activation energies of 59.06 kJ/mol and 57.33 kJ/mol, respectively. The mineral phase transformation and morphological analysis were studied by X-ray diffractometer and scanning electron microscope. The results indicated that rare-earth fluoride (REF₃) reacts with sodium hydroxide to form rare-earth hydroxide (RE(OH)₃) and soluble sodium fluoride (NaF), while LiF is converted into LiOH and enters the liquid phase. High-efficiency separation was achieved by washing with water, avoiding high-temperature energy consumption and the problem of fluorine-containing waste gas. Full article

Catalyzing hydrogen evolution reaction (HER) is a key process in high-efficiency proton exchange membrane water electrolysis (PEMWE) devices. To replace the use of Pt-based HER catalyst, tungsten carbide (W₂C) is one of the most promising non-noble-metal-based catalysts with low cost, replicable catalytic performance, and durability. However, the preparation access to scalable production of W₂C catalysts is inevitable. Herein, we introduced a facile protocol to achieve the tungsten carbide species by plasma treatment under a CH₄ atmosphere from the WO₃ precursor. Moreover, the heterogeneous structure of the tungsten carbide/tungsten oxide nanosheets further enhances the catalytic activity for HER with the enlarged specific surface area and the synergism on the interfaces. The prepared tungsten carbide/tungsten oxide heterostructure nanosheets (WO_3-x-850-P) exhibit exceptional HER catalytic activity and stable longevity in acid electrolytes. This work provides a facile and effective method to construct high-performance and non-precious-metal-based electrocatalysts for industrial-scale water electrolysis. Full article

As one core component in hydrogen fuel cells and water electrolysis cells, bipolar plates (BPs) perform multiple important functions, such as separating the fuel and oxidant flow, providing mechanical support, conducting electricity and heat, connecting the cell units into a stack, etc. On the path toward commercialization, the manufacturing costs of bipolar plates have to be substantially reduced by adopting low-cost and easy-to-process metallic materials (e.g., stainless steel, aluminum or copper). However, these materials are susceptible to electrochemical corrosion under harsh operating conditions, resulting in long-term performance degradation. By means of advanced thermal spraying technologies, protective coatings can be prepared on bipolar plates so as to inhibit oxidation and corrosion. This paper reviews several typical thermal spraying technologies, including atmospheric plasma spraying (APS), vacuum plasma spraying (VPS) and high-velocity oxygen fuel (HVOF) spraying for preparing coatings of bipolar plates, particularly emphasizing the effect of spraying processes on coating effectiveness. The performance of coatings relies not only on the materials as selected or designed but also on the composition and microstructure practically obtained in the spraying process. The temperature and velocity of in-flight particles have a significant impact on coating quality; therefore, precise control over these factors is demanded. Full article

This research investigated the suitability of air-to-water generator (AWG) technology to address one of the main concerns in green hydrogen production, namely water supply. This study specifically addresses water quality and energy sustainability issues, which are crucial research questions when AWG technology is intended for electrolysis. To this scope, a reasoned summary of the main findings related to atmospheric water quality has been provided. Moreover, several experimental chemical analyses specifically focused on meeting electrolysis process requirements, on water produced using a real integrated AWG system equipped with certified materials for food contact, were discussed. To assess the energy sustainability of AWGs in green hydrogen production, a case study was presented regarding an electrolyzer plant intended to serve as energy storage for a 2 MW photovoltaic field on Iriomote Island. The integrated AWG, used for the water quality analyses, was studied in order to determine its performance in the specific island climate conditions. The production exceeded the needs of the electrolyzer; thus, the overproduction was considered for the panels cleaning due to the high purity of the water. Due to such an operation, the efficiency recovery was more than enough to cover the AWG energy consumption. This paper, on the basis of the quantity results, provides the first answers to the said research questions concerning water quality and energy consumption, establishing the potential of AWG as a viable solution for addressing water scarcity, and enhancing the sustainability of electrolysis processes in green hydrogen production. Full article

Hydrogen is a prospective energy carrier because there are practically no gaseous emissions of greenhouse gases in the atmosphere during its use as a fuel. The great benefit of hydrogen being a practically inexhaustible carbon-free fuel makes it an attractive alternative to fossil fuels. I.e., there is a circular process of energy recovery and use. Another big advantage of hydrogen as a fuel is its high energy content per unit mass compared to fossil fuels. Nowadays, hydrogen is broadly used as fuel in transport, including fuel cell applications, as a raw material in industry, and as an energy carrier for energy storage. The mass exploitation of hydrogen in energy production and industry poses some important challenges. First, there is a high price for its production compared to the price of most fossil fuels. Next, the adopted traditional methods for hydrogen production, like water splitting by electrolysis and methane reforming, lead to the additional charging of the atmosphere with carbon dioxide, which is a greenhouse gas. This fact prompts the use of renewable energy sources for electrolytic hydrogen production, like solar and wind energy, hydropower, etc. An important step in reducing the price of hydrogen as a fuel is the optimal design of supply chains for its production, distribution, and use. Another group of challenges hindering broad hydrogen utilization are storage and safety. We discuss some of the obstacles to broad hydrogen application and argue that they should be overcome by new production and storage technologies. The present review summarizes the new achievements in hydrogen application, production, and storage. The approach of optimization of supply chains for hydrogen production and distribution is considered, too. Full article

This paper presents the potentials and costs of synthetic fuels (synfuels) produced by renewable energy via PEM water electrolysis and the subsequent Fischer–Tropsch process for the years 2020, 2030, 2040, and 2050 in selected countries across the globe. The renewable energy potential was determined by the open-source tool pyGRETA and includes photovoltaic, onshore wind, and biomass. Carbon dioxide is obtained from biomass and the atmosphere by direct air capture. The potentials and costs were determined by aggregating minimal cost energy systems for each location on a state level. Each linear energy system was modelled and optimised by the optimisation framework urbs. The analysis focused on decentralised and off-grid synthetic fuels’ production. The transportation costs were roughly estimated based on the distance to the nearest maritime port for export. The distribution infrastructure was not considered since the already-existing infrastructure for fossil fuels can be easily adopted. The results showed that large amounts of synthetic fuels are available for EUR 110/MWh (USD 203/bbl) mainly in Africa, Central and South America, as well as Australia for 2050. This corresponds to a cost reduction of more than half compared to EUR 250/MWh (USD 461/bbl) in 2020. The synfuels’ potentials follow the photovoltaic potentials because of the corresponding low levelised cost of electricity. Batteries are in particular used for photovoltaic-dominant locations, and transportation costs are low compared to production costs. Full article

There is a significant push to reduce carbon dioxide (CO₂) emissions and develop low-cost fuels from renewable sources to replace fossil fuels in applications such as energy production. As a result, CO₂ conversion has gained widespread attention as it can reduce the accumulation of CO₂ in the atmosphere and produce fuels and valuable industrial chemicals, including carbon monoxide, alcohols, and hydrocarbons. At the same time, finding ways to store energy in batteries or energy carriers such as hydrogen (H₂) is essential. Water electrolysis is a powerful technology for producing high-purity H₂, with negligible emission of greenhouse gases, and compatibility with renewable energy sources. Additionally, the electrolysis of organic compounds, such as lignin, is a promising method for localised H₂ production, as it requires lower cell voltages than conventional water electrolysis. Industrial wastewater can be employed in those organic electrolysis systems due to their high organic content, decreasing industrial pollution through wastewater disposal. Electrocoagulation, indirect electrochemical oxidation, anodic oxidation, and electro-Fenton are effective electrochemical methods for treating industrial wastewater. Furthermore, bioenergy technology possesses a remarkable potential for producing H₂ and other value-added chemicals (e.g., methane, formic acid, hydrogen peroxide), along with wastewater treatment. This paper comprehensively reviews these approaches by analysing the literature in the period 2012–2022, pointing out the high potential of using electrolytic cells for energy and environmental applications. Full article

The poor reversibility and slow reaction kinetics of catalytic materials seriously hinder the industrialization process of proton exchange membrane (PEM) water electrolysis. It is necessary to develop high-performance and low-cost electrocatalysts to reduce the loss of reaction kinetics. In this study, a novel catalyst support featured with porous surface structure and good electronic conductivity was successfully prepared by surface modification via a thermal nitriding method under ammonia atmosphere. The morphology and composition characterization-confirmed that a TiN layer with granular porous structure and internal pore-like defects was established on the Ti sheet. Meanwhile, the conductivity measurements showed that the in-plane electronic conductivity of the as-developed material increased significantly to 120.8 S cm⁻¹. After IrO_x was loaded on the prepared TiN-Ti support, better dispersion of the active phase IrO_x, lower ohmic resistance, and faster charge transfer resistance were verified, and accordingly, more accessible catalytic active sites on the catalytic interface were developed as revealed by the electrochemical characterizations. Compared with the IrO_x/Ti, the as-obtained IrO_x/TiN-Ti catalyst demonstrated remarkable electrocatalytic activity (${\eta }_{{10\mathrm{mA}\mathrm{cm}}^{-2}}$= 302 mV) and superior stability (overpotential degradation rate: 0.067 mV h⁻¹) probably due to the enhanced mass adsorption and transport, good dispersion of the supported active phase IrO_x, increased electronic conductivity and improved corrosion resistance provided by the TiN-Ti support. Full article

Molecular hydrogen (H₂) is considered one of the most promising fuels to decarbonize the industrial and transportation sectors, and its photocatalytic production from molecular catalysts is a research field that is still abounding. The search for new molecular catalysts for H₂ production with simple and easily synthesized ligands is still ongoing, and the terpyridine ligand with its particular electronic and coordination properties, is a good candidate to design new catalysts meeting these requirements. Herein, we have isolated the new mono-terpyridyl rhodium complex, [Rh^III(tpy)(CH₃CN)Cl₂](CF₃SO₃) (Rh-tpy), and shown that it can act as a catalyst for the light-induced proton reduction into H₂ in water in the presence of the [Ru(bpy)₃]Cl₂ (Ru) photosensitizer and ascorbate as sacrificial electron donor. Under photocatalytic conditions, in acetate buffer at pH 4.5 with 0.1 M of ascorbate and 530 μM of Ru, the Rh-tpy catalyst produces H₂ with turnover number versus catalyst (TON_Cat*) of 300 at a Rh concentration of 10 μM, and up to 1000 at a concentration of 1 μM. The photocatalytic performance of Ru/Rh-tpy/HA^–/H₂A has been also compared with that obtained with the bis-dimethyl-bipyridyl complex [Rh^III(dmbpy)₂Cl₂]⁺ (Rh2) as a catalyst in the same experimental conditions. The investigation of the electrochemical properties of Rh-tpy in DMF solvent reveals that the two-electrons reduced state of the complex, the square-planar [Rh^I(tpy)Cl] (Rh^I-tpy), is quantitatively electrogenerated by bulk electrolysis. This complex is stable for hours under an inert atmosphere owing to the π-acceptor property of the terpyridine ligand that stabilizes the low oxidation states of the rhodium, making this catalyst less prone to degrade during photocatalysis. The π-acceptor property of terpyridine also confers to the Rh-tpy catalyst a moderately negative reduction potential (Ep_c(Rh^III/Rh^I) = −0.83 V vs. SCE in DMF), making possible its reduction by the reduced state of Ru, [Ru^II(bpy)(bpy^•−)]⁺ (Ru⁻) (E_1/2(Ru^II/Ru⁻) = −1.50 V vs. SCE) generated by a reductive quenching of the Ru excited state (*Ru) by ascorbate during photocatalysis. A Stern–Volmer plot and transient absorption spectroscopy confirmed that the first step of the photocatalytic process is the reductive quenching of *Ru by ascorbate. The resulting reduced Ru species (Ru⁻) were then able to activate the Rh^III-tpy H₂-evolving catalyst by reduction generating Rh^I-tpy, which can react with a proton on a sub-nanosecond time scale to form a Rh^III(H)-tpy hydride, the key intermediate for H₂ evolution. Full article

The increasing trend in global energy demand has led to an extensive use of fossil fuels and subsequently in a marked increase in atmospheric CO₂ content, which is the main culprit for the greenhouse effect. In order to successfully reverse this trend, many schemes for CO₂ mitigation have been proposed, taking into consideration that large-scale decarbonization is still infeasible. At the same time, the projected increase in the share of variable renewables in the future energy mix will necessitate large-scale curtailment of excess energy. Collectively, the above crucial problems can be addressed by the general scheme of CO₂ hydrogenation. This refers to the conversion of both captured CO₂ and green H₂ produced by RES-powered water electrolysis for the production of added-value chemicals and fuels, which are a great alternative to CO₂ sequestration and the use of green H₂ as a standalone fuel. Indeed, direct utilization of both CO₂ and H₂ via CO₂ hydrogenation offers, on the one hand, the advantage of CO₂ valorization instead of its permanent storage, and the direct transformation of otherwise curtailed excess electricity to stable and reliable carriers such as methane and methanol on the other, thereby bypassing the inherent complexities associated with the transformation towards a H₂-based economy. In light of the above, herein an overview of the two main CO₂ abatement schemes, Carbon Capture and Storage (CCS) and Carbon Capture and Utilization (CCU), is firstly presented, focusing on the route of CO₂ hydrogenation by green electrolytic hydrogen. Next, the integration of large-scale RES-based H₂ production with CO₂ capture units on-site industrial point sources for the production of added-value chemicals and energy carriers is contextualized and highlighted. In this regard, a specific reference is made to the so-called Power-to-X schemes, exemplified by the production of synthetic natural gas via the Power-to-Gas route. Lastly, several outlooks towards the future of CO₂ hydrogenation are presented. Full article

Water contamination due to various nitrogenous pollutants generated from wastewater treatment plants is a crucial and ubiquitous environmental problem now-a-days. Nitrogen contaminated water has manifold detrimental effects on human health as well as aquatic life. Consequently, various biological treatment processes are employed to transform the undesirable forms of nitrogen in wastewater to safer ones for subsequent discharge. In this review, an overview of various conventional biological treatment processes (viz. nitrification, denitrification, and anammox) have been presented along with recent novel bioelectrochemical methods (viz. microbial fuel cells and microbial electrolysis cells). Additionally, nitrogen is an indispensable nutrient necessary to produce artificial fertilizers by fixing dinitrogen gas from the atmosphere. Thus, this study also explored the potential capability of various nitrogen recovery processes from wastewater (like microalgae, cyanobacteria, struvite precipitation, stripping, and zeolites) that are used in industries. Further, the trade-offs, challenges posed by these processes have been dwelt on along with other biological processes like CANON, SHARON, OLAND, and others. Full article

Low-temperature electrolysis by using polymer electrolyte membranes (PEM) can play an important role in hydrogen energy transition. This work presents a study on the performance of a proton exchange membrane in the water electrolysis process at room temperature and atmospheric pressure. In the perspective of applications that need a device with small volume and low weight, a miniaturized electrolysis cell with a 36 cm² active area of PEM over a total surface area of 76 cm² of the device was used. H₂ and O₂ production rates, electrical power, energy efficiency, Faradaic efficiency and polarization curves were determined for all experiments. The effects of different parameters such as clamping pressure and materials of the electrodes on polarization phenomena were studied. The PEM used was a catalyst-coated membrane (Ir-Pt-Nafion™ 117 CCM). The maximum H₂ production was about 0.02 g min⁻¹ with a current density of 1.1 A cm⁻² and a current power about 280 W. Clamping pressure and the type of electrode materials strongly influence the activation and ohmic polarization phenomena. High clamping pressure and electrodes in titanium compared to carbon electrodes improve the cell performance, and this results in lower ohmic and activation resistances. Full article

Hydrogen is an environmentally friendly biofuel which, if widely used, could reduce atmospheric carbon dioxide emissions. The main barrier to the widespread use of hydrogen for power generation is the lack of technologically feasible and—more importantly—cost-effective methods of production and storage. So far, hydrogen has been produced using thermochemical methods (such as gasification, pyrolysis or water electrolysis) and biological methods (most of which involve anaerobic digestion and photofermentation), with conventional fuels, waste or dedicated crop biomass used as a feedstock. Microalgae possess very high photosynthetic efficiency, can rapidly build biomass, and possess other beneficial properties, which is why they are considered to be one of the strongest contenders among biohydrogen production technologies. This review gives an account of present knowledge on microalgal hydrogen production and compares it with the other available biofuel production technologies. Full article