Renewable Sources Of Hydrogen Research Articles

Front Cover: Conversion of Cellobiose to Formic Acid as a Biomass‐Derived Renewable Hydrogen Source Using Solid Base Catalysts (ChemistryOpen 11/2024)

Front Cover: Conversion of Cellobiose to Formic Acid as a Biomass‐Derived Renewable Hydrogen Source Using Solid Base Catalysts (ChemistryOpen 11/2024)

Conversion of Cellobiose to Formic Acid as a Biomass-Derived Renewable Hydrogen Source Using Solid Base Catalysts.

Formic acid is considered a promising hydrogen carrier. Biomass-derived formic acid can be obtained by oxidative decomposition of sugars. This study explored the production of formic acid from cellobiose, a disaccharide consisting of d-glucose linked by β-glycosidic bonds using heterogeneous catalysts under mild reaction conditions. The use of alkaline earth metal oxide solid base catalysts like CaO and MgO in the presence of hydrogen peroxide could afford formic acid from cellobiose at 343 K. While CaO gave 14 % yield of formic acid, the oxide itself was converted to a harmful metal peroxide, CaO2 after the reaction. In contrast, MgO could produce formic acid without the formation of the metal peroxide. The difficulty in selectively synthesizing formic acid from cellobiose using these solid base catalysts was due to the poor conversion of cellobiose to glucose. Using a combination of solid acid and base catalysts, a high formic acid yield of 33 % was obtained under mild reaction conditions due to the quantitative hydrolysis of cellobiose to glucose by a solid acid followed by the selective decomposition of glucose to formic acid by a solid base.

High activities of nickel (II) complexes containing phosphorus-nitrogen ligands in hydrogen transfer reaction of imines using formic acid as a renewable hydrogen source

The catalytic reduction of imines to obtain secondary amines is an important route in the synthesis of molecules of biological or pharmaceutical interest. A series of new nickel (II) complexes bearing phosphorous-nitrogen (P,N) or phosphorous-nitrogen-phosphorous (P,N,P) ligands were characterized and studied as catalysts in hydrogen transfer reaction of imines, using formic acid as a hydrogen source, while avoiding the use of molecular hydrogen (H2). The complexes, of general formula NiCl2(L), [Ni(L)2](CF3SO3)2 (in which L is a P,N ligand) and [NiCl(L)]Cl (in the case of a tridentate PNP ligand), were active catalysts in the imine hydrogen, with turnover frequencies (TOF) up to 373 h−1 with NiCl2L1 complex (L1 = 2-(diphenylphosphinoamino) pyridine) and N-benzylideneaniline as substrate, while a [Ni(L)2](CF3SO3)2 complex bearing the same P,N ligand achieved a slightly lower activity (TOF = 320 h−1). Catalyst recyclability was also studied, achieving near full conversion after four cycles, with a total substrate/catalyst ratio of 1000:1.

Zeolite-encaged mononuclear copper centers catalyze CO2 selective hydrogenation to methanol.

The selective hydrogenation of CO2 to methanol by renewable hydrogen source represents an attractive route for CO2 recycling and is carbon neutral. Stable catalysts with high activity and methanol selectivity are being vigorously pursued, and current debates on the active site and reaction pathway need to be clarified. Here, we report a design of faujasite-encaged mononuclear Cu centers, namely Cu@FAU, for this challenging reaction. Stable methanol space-time-yield (STY) of 12.8mmol gcat-1 h-1 and methanol selectivity of 89.5% are simultaneously achieved at a relatively low reaction temperature of 513K, making Cu@FAU a potential methanol synthesis catalyst from CO2 hydrogenation. With zeolite-encaged mononuclear Cu centers as the destined active sites, the unique reaction pathway of stepwise CO2 hydrogenation over Cu@FAU is illustrated. This work provides a clear example of catalytic reaction with explicit structure-activity relationship and highlights the power of zeolite catalysis in complex chemical transformations.

Transfer hydrogenation of pyridinium and quinolinium species using ethanol as a hydrogen source to access saturated N-heterocycles.

Catalytic transfer hydrogenation (TH) for the reduction of heterocycles is an emerging strategy for accessing biologically active saturated N-heterocycles. Herein, we report a TH protocol that utilizes ethanol as a renewable hydrogen source and an Ir catalyst for the reduction of quinolines and pyridines. The reaction is promoted by simple amides as ligands.

Oxidative Conversion of Glucose to Formic Acid as a Renewable Hydrogen Source Using an Abundant Solid Base Catalyst.

Formic acid is one of the most desirable liquid hydrogen carriers. The selective production of formic acid from monosaccharides in water under mild reaction conditions using solid catalysts was investigated. Calcium oxide, an abundant solid base catalyst available from seashell or limestone by thermal decomposition, was found to be the most active of the simple oxides tested, with formic acid yields of 50 % and 66 % from glucose and xylose, respectively, in 1.4 % H2O2 aqueous solution at 343 K for 30 min. The main reaction pathway is a sequential formation of formic acid from glucose by C−C bond cleavage involving aldehyde groups in the acyclic form. The reaction also involves base‐catalyzed aldose‐ketose isomerization and retroaldol reaction, resulting in the formation of fructose and trioses including glyceraldehyde and dihydroxyacetone. These intermediates were further decomposed into formic acid or glycolic acid. The catalytic activity remained unchanged for further reuse by a simple post‐calcination.

Selection of Hydrogen Donors for the Production of Renewable Diesel by in Situ Catalytic Deoxygenation of Palm Oil

Recently, advanced biofuels have gained interest and importance; as a result, the world production of renewable diesel has quadrupled in the last 5 years. Renewable diesel is a type of biodiesel whose functional properties are similar, or even superior, to those of fossil diesel. It also looks more attractive than conventional biodiesel (FAME), as an option for the partial or complete replacement of liquid fossil fuels in the effort to reduce GHG emissions generated in the transport sector of diesel engines. However, when obtained by hydrotreating, the use of gaseous hydrogen makes the process lose sustainability due to its petrochemical origin (at least 90% comes from the reforming of naphtha) and high risk in its safe handling, besides increasing the costs due to its intensive operating conditions (temperature and pressure). A possible solution to this remarkable disadvantage is the generation of hydrogen in situ, which can be carried out by hydrogenation by catalytic transfer, using a donor, usually a solvent that transfers hydrogen. This is an interesting alternative for the hydrogenation of organic compounds, with substantial advantages over processes that use molecular hydrogen, in addition to moderate process conditions and reduction of the intensive energy consumption. In this sense, it is necessary to evaluate potential donors as renewable sources of hydrogen to obtain renewable diesel from palm oil. To carry out the previous analysis, in this study, a multicriteria decision method (MACBETH) is applied, using criteria such as renewable origin, decomposition products, cost, availability and toxicity, which are considered to select the most appropriate family of organic compounds that act as hydrogen donor: alcohols, polyols, aldehydes, ketones, carboxylic acids, condensed aromatic homologs, amines and alkanes. Results show that alcohols, polyols and carboxylic acids are the most suitable organic families for the generation of hydrogen in situ during hydroprocessing. According to sustainability and taking into account the atomic economy, the availability and biorefinery origin, it was found that the most promising compounds to use as donors in each of these families are the ethanol, glycerine and formic acid, which are then evaluated using thermodynamic analysis.

(Invited) HydroGEN Benchmarking: Developing Best Practices for Water Splitting Technologies

The need for renewable sources of hydrogen is increasing rapidly based on global goals for decarbonization. Interest and investment has also increased with the advent of the Hydrogen Council and the DOE H2@Scale initiative. There are several pathways which could eventually be part of the overall mix, but are currently at different maturities and have different challenges. Low cost renewable energy provides a potential pathway for low temperature electrolysis to make a large impact in the short term, while high temperature baseload such as nuclear matches well with high temperature electrolysis based on solid oxide technology. Photoelectrochemcal and solar thermal chemical water splitting are earlier stage technologies, but could be viable in the long term especially in areas without current infrastructure, if the materials targets can be achieved and manufacturing capability is developed. In the nearer term, understanding of these challenges can also provide valuable perspective for the more mature pathways. In any of these technologies, appropriate comparisons of test results is important to measure overall progress in the field and identify promising directions, as well as to provide credibility to published results. The DOE Fuel Cell Technologies Office previously funded the development of a detailed reference guide of common methodologies, protocols, and important limitations for measuring critical performance properties of advanced hydrogen storage materials, which has served as a resource to the hydrogen storage materials development community to aid in clearly communicating the relevant performance properties of new materials as they are discovered and tested. The project was coordinated with the IEA and involved 46 co-authors and contributors from 9 countries. The final documents are available to the public on-line: https://www.energy.gov/eere/fuelcells/downloads/recommended-best-practices-characterization-storage-properties-hydrogen-0 A similar effort is now underway for water splitting technologies, framed by questionnaires distributed to the community, frameworks for materials and device testing, and workshops and discussions for feedback. A series of protocols is being drafted to provide easy to follow procedures for materials characterization. The team is also identifying gaps in methods and materials for possible development, and drafting technology roadmaps to highlight research needs. This talk will describe the success of the storage effort, and status for the water splitting benchmarking project.

Performance evaluation of biogas upgrading systems from swine farm to biomethane production for renewable hydrogen source

Biogas upgrading to biomethane is a necessary process for biohydrogen production from renewable source. In this work, absorption processes using water and diethanolamine (DEA) as absorbent were modeled in Aspen Plus software. The purpose was to find the optimal operating condition for sustainable production of biomethane using multi-criteria perspective considering technical, environmental and economic aspects. The absorption system was modified by including one additional absorber unit for improving biogas upgrading efficiency. The performance of the biogas upgrading system was evaluated and compared in terms of methane recovery, methane content in biomethane, and energy consumption. Effects of operating conditions such as operating pressure in absorber, concentration, and total flow rate of absorbents were investigated. The results revealed that the performance of the modified absorption system was superior to the conventional system. The methane content in biomethane, methane recovery, and energy consumption increased with the increase of operating pressure in the absorbers. Increasing concentration and total flow rate of absorbents increased the methane content in biomethane and the energy consumption but decreased the methane recovery. The optimal operating condition could achieve 96%v/v of methane content in biomethane with methane recovery of higher than 95%v/v in the modified water absorption system. The optimum operating pressures of absorber Units 1 and 2, and total absorbent flow rates were at 13 and 5 bar and 16,000 kmol/h, respectively.

Perspectives on Low-Temperature Electrolysis and Potential for Renewable Hydrogen at Scale.

Hydrogen is an important part of any discussion on sustainability and reduction in emissions across major energy sectors. In addition to being a feedstock and process gas for many industrial processes, hydrogen is emerging as a fuel alternative for transportation applications. Renewable sources of hydrogen are therefore required to increase in capacity. Low-temperature electrolysis of water is currently the most mature method for carbon-free hydrogen generation and is reaching relevant scales to impact the energy landscape. However, costs still need to be reduced to be economical with traditional hydrogen sources. Operating cost reductions are enabled by the recent availability of low-cost sources of renewable energy, and the potential exists for a large reduction in capital cost withmaterial and manufacturing optimization. This article focuses on the current status and development needs by component for the low-temperature electrolysis options.

Application of Acoustic Emission to Study Electrochemical Energy Conversion and Storage Devices

Electrochemical energy conversion and storage devices find wide application in industry, transportation, and consumer goods. Due to the varying requirements of these different applications, there is no one size fits all solution and technologies of interest span from electrolyser and fuel cell technology to batteries such as Li-ion and Li-S. The future of the ‘Hydrogen Economy’ is contingent on establishing renewable sources of hydrogen, and electrolysers are a key technology to fulfil this goal. Polymer electrolyte membrane (PEM) technology, widely adopted in fuel cells, is of special significance to electrolysers due to numerous advantages over alternatives such as alkaline electrolysers; developments in PEM fuel cell technology can be rapidly applied to water electrolysers due to similarities in materials and electrode architecture. Lithium-based batteries are a complementary energy storage technology, used in numerous fields such as electronics, medical devices, and the automotive industry. During the operation of these energy conversion and storage devices, complex chemical and mechanical processes occur, each with specific significance to lifetime, performance, and safety. In electrolysers, two-phase flow occurs in the flow channels and gas diffusion layers and electrochemical activity occurs at the catalyst layer. In Li-ion batteries, the intercalation of Li ions into negative and positive electrode, cracking of electrode materials, the formation of gas bubbles due to electrolyte decomposition and solid electrolyte interphase (SEI) formation are processes of great importance. Various approaches have been described in order to monitor and investigate these processes, e.g. X-ray computed tomography, scanning electron microscopy and electrochemical methods. However, diagnostic tools often come with specific drawbacks: high costs, no possibility for in-situ measurements or destructive measurements. These issues call for novel diagnostic techniques, which allows for fast, low-cost, in-situ and non-destructive measurements. This work describes the use of acoustic emission (AE) as a diagnostic technique for electrochemical energy storage devices. In AE, a piezoelectric sensor is used to detect mechanical perturbations from a sample. By comparing the amount of acoustic activity, its duration, energy, and frequency spectrum, conclusions can be drawn regarding the nature of the observed process. In this work, we have successfully demonstrated the potential of acoustic emission as a diagnostic tool for PEM water electrolysers; in particular to study two-phase flow within the flow channels during gas formation. A close link between bubble size and number within the flow channel of a PEM water electrolyser and the AE measured on the surface of the end plates has been established. Two locations along the flow channel were investigated through AE measurements and high-speed visual imaging. For the upper location, AE measurements showed that the number of acoustic hits reaches a maximum around 0.5 A cm2 and decreases before reaching a plateau at higher current densities. The average frequency of these hits decreases with current density, which can be attributed to an increase in average bubble size. High-speed imaging at the upper location is consistent with the acoustic emission results. The number of bubbles detected follows the same trend as the number of acoustic hits with current density. This implies that AE can monitor relative changes in the number of bubbles flowing through an electrolyser and can, therefore, detect changes in flow regime. Image analysis also showed a trend towards increasing bubble size at higher current densities, which supports the frequency data from acoustic emission; hence, AE can be used to detect changes in bubble size in a PEM electrolyser. Furthermore, AE was used to monitor processes in Li-ion and Li-S batteries during charge and discharge. In Li-ion cells, strong acoustic activity was found between 3.7 and 4.0 V during the first cycles, a voltage range which is related to electrolyte decomposition and gas evolution. An increased number of AE hits has also been found during SEI formation. In Li-S batteries, AE events were demonstrated to coincide with the chemical transformation between different polysulphide species.

Hydrogenation of N-benzylideneaniline by palladium (II) catalysts with phosphorus-nitrogen ligands using formic acid as a renewable hydrogen source

This paper reports the hydrogenation of N-benzylideneaniline catalysed by Pd(II) compounds containing heterobidentated phosphorus-nitrogen (PN) ligands. The general formulas of the catalysts are cis-[PdCl2(L1)] and [PdCl(PPh3)(L1)]Cl (where L1= Ph2PCH2py, Ph2PNCH3py, Ph2PNHpy, Ph2PNHpym and Ph2Pqn). The hydrogenation of N-benzylideneaniline was carried out using propan-2-ol or formic acid as the hydrogen source. The catalytic activity was studied under different conditions by varying the base (NaOH and tert-butoxide) and the base/catalyst ratio (B/C = 20/1 and 50/1.Additionally, triethylamine was also used with a base/catalyst ratio of B/C = 500/1. It was found that palladium catalysts containing hemilabile heterobidentated ligands showed high catalytic activity and selectivity for the hydrogenation of N-benzylideneaniline. The catalysts cis-[PdCl2(Ph2PNHPy)] (2) and [PdCl(Ph2Pqn)(PPh3)]Cl (6) maintained the activities when the reactor was recharged with a fresh substrate (1000/1 substrate/catalyst ratio). It was also found that catalytic hydrogenation works well with only formic acid, with its activities ranging close to 100% for the 2 and 6 complexes.

Synthesis of jet fuel rang cycloalkane from isophorone with glycerol as a renewable hydrogen source

For the first time, 1,​1,​3-​trimethyl-cyclohexane (a jet fuel range cycloalkane) was synthesized by coupling the aqueous phase reforming (APR) of glycerol and the hydrodeoxygenation (HDO) of isophorone which can be obtained from lignocellulose. Among the investigated catalysts, Pt/Al2O3 was found to be the most active for the production of 1,​1,​3-​trimethyl-cyclohexane with the hydrogen which was in-situ generated by the APR of glycerol. Over it, high carbon yield (67.0%) of 1,​1,​3-​trimethyl-cyclohexane can be achieved at 533K in the absence of external hydrogen. The excellent performance of Pt/Al2O3 catalyst can be explained because Pt is highly active for both APR and HDO reactions. Besides glycerol, many other lignocellulose derived polylols (such as ethylene glycol, xylitol and sorbitol) and methanol can also be used as renewable hydrogen source for the HDO of isophorone. As a potential application, the 1,​1,​3-​trimethyl-cyclohexane as obtained can be blended into the conventional jet fuels to improve their volumetric heat values.

Metal decorated carbon nanotubes for electrocatalytic water splitting

Water is the most abundant, renewable source of hydrogen on our planet. Appropriate catalytic materials are needed to minimize the energy required to electrochemically split the water molecule, and electrode with high specific areas are sought to maximize the electrolyte/electrode interface. We use Carbon Nanotubes (CNTs) bundles as templates for water splitting electrodes fabrication. Appropriate catalyst materials are thermally evaporated on CNTs, to exploit both their good electrical conductivity and large specific area, while optimizing over-potential towards Hydrogen Evolving Reaction (HER) or Oxygen Evolving Reaction (OER) through the deposited catalysts. Electrodes morphology and surface chemistry are characterized, before and after electrolysis, by means of scanning electron microscopy and X-ray photoelectron spectroscopy. Our electrodes are able to perform water oxidation and water reduction near their thermo-dynamical limit. Performances of these electrodes, taking into account the extremely low loading mass of catalytic material (10−2 mg cm−2) with respect to other reported systems, are among the best HER and OER system reported so far. Finally, a working electrolyser, capable to operate at the interesting low voltage of a single AA battery (1.5 V) and output a stable current (>2.0 mA cm−2) for at least 20 h, is successfully assembled and tested.

Effects of TiO2 Nanoparticle Size on Solar-to-Hydrogen Efficiency in Photoelectrochemical Cells

The photocatalytic splitting of water into oxygen and hydrogen using solar light is a promising clean and renewable source of hydrogen fuel. TiO2 is one of the most studied and promising photocatalysts. Nanoparticle sizes ranging from 100 nm down to 5 nm were tested using photoelectrochemical (PEC) measurements. The TiO2 powders were characterized using XRD to determine crystal phase. A 2-electrode system was utilized in order to measure solar to hydrogen efficiency (STH) related to whole cell efficiency in the alkaline aqueous electrolyte. The optimum particle size in term of STH efficiency was 30 nm. Also, it was revealed that choosing anatase phase of TiO2 powder would increase the STH efficiency.

Water Splitting: One‐dimensional TiO2 Nanotube Photocatalysts for Solar Water Splitting (Adv. Sci. 1/2017)

The rapid development of globalization and industrialization has caused a series of environment problems due to the increased consumption of fossil energy sources. To address these concerns, water splitting for hydrogen production in the presence of a semiconductor photocatalyst is studied extensively as a potential method to provide clean and renewable hydrogen source. In article 1600152, Yuekun Lai and co-workers review various methods to construct 1D TiO2 nanotubes, and modified strategies to enhance solar light harvesting and energy conversion efficiency. Furthermore, the mechanism and applications of photo/photoelectro-catalytic water splitting are comprehensively discussed.

Analysis of an Integrated Agro-waste Gasification and 120 kW SOFC CHP System: Modeling and Experimental Investigation

Renewable sources of hydrogen are of major interest in the context of energy production through fuel cells. The technical feasibility of CHP system composed by orange peels steam/air gasification unit coupled with a solid oxide fuel cell (SOFC) was investigated in this study. To this purpose, a zero-dimensional process simulation model of the CHP system using Aspen Plus was developed. Mathematical model was experimentally validated in a lab scale apparatus. Moreover, optimal operative conditions and integration options were investigated, as well as the system maximum theoretical overall efficiency. Results showed that in order to obtain 120kW of DC power from the specific SOFC, 65kg/h of biomass with 20% of moisture and 173kg/h of raw biomass with 70% of water needed to be fed in the CHP system. It was theoretically proved that 120kW of DC power and 135kW of heat could be produced from SOFC unit at the selected operative conditions, with a net CHP maximum efficiency equal to 74%.

Isothermal reverse water gas shift chemical looping on La0.75Sr0.25Co(1−Y)FeYO3 perovskite-type oxides

The RWGS-CL is a two-step process for the conversion of CO2 to CO using a redox cycle of a parent metal oxide. Previously, this process was demonstrated using La0.75Sr0.25CoO3 perovskite, but this material required different oxidation and reduction temperatures. In this study, oxidation and reduction were achieved at the same temperature. La0.75Sr0.25Co(1−Y)FeYO3 (Y=0, 0.5, 0.75 and 1) perovskite-type oxides were synthesized by the Pechini method and were tested by X-ray diffraction (XRD), temperature-programmed reduction (H2-TPR) and oxidation with carbon dioxide (CO2-TPO). Results demonstrated that the LaFeO3 (Y=1) sample showed structure stability when reduced at 550°C, the lowest CO formation onset temperature (450°C) and high selectivity toward CO. Five isothermal RWGS-CL cycles were performed at 550°C on the Y=1 sample. The stability of the crystalline structure throughout the cycles was demonstrated by XRD. CO formation rates increased during the first cycles and stabilized at the third cycle due to the increased accumulated amount of oxygen vacancies (δ) on the perovskite surface, which is consistent with the findings from the density functional theory studies that directly correlate the CO2 binding strength to the amount of oxygen vacancies. The high CO formation rates and the repeatability of the process make RWGS-CL a promising technology for CO2 conversion, if a renewable hydrogen source is available.

Hydrogen production by reforming of acetic acid using La–Ni type perovskites partially substituted with Sm and Pr

The condensation of gases from the pyrolysis of biomass leads to a liquid compound called bio-oil. This oil can be divided into two fractions: one aqueous and another non-aqueous. The aqueous fraction does not have a high market value and it is usually discarded. However, this mixture has considerable amounts of organic compounds, which can be potential renewable sources of hydrogen. Steam reforming has been the most studied reaction to produce hydrogen from the aqueous fraction of bio-oil. Due to the diversity of organic compounds found in this aqueous fraction, model compounds have usually been used to study this mixture. Among the compounds used to represent the aqueous fraction of bio-oil, acetic acid is the most popular. Nickel-based catalysts are traditionally used for reforming reactions. An alternative to combine high Ni content employed in catalysts, this kind of process with desirable values of dispersion is to use perovskite-type precursors (LaNiO3). Therefore, the objective of this study was to investigate the production of hydrogen from the aqueous fraction of bio-oil. More specifically, in this work, LaNiO3, LaPrNiO3 and LaSmNiO3 were tested as precursors for catalysts in the reaction of steam and oxidative reforming of acetic acid. During the reaction, the catalysts showed the formation of the same products: H2, CO, CH4, CO2, C3H6O, but with different selectivities. All samples presented good selectivity for hydrogen formation, and the presence of Pr and Sm just slightly affected the catalytic performance. Due to the large accumulations of coke observed during the reaction of steam reforming, a small amount of O2 was added to the mixture. The presence of this oxidant improved catalytic activity without reducing the amount of hydrogen produced. Furthermore, it helped to reduce the deposits of coke, maintaining the catalytic activity during 24h of reaction.

Bio-fuel reforming for solid oxide fuel cell applications. Part 2: Biodiesel

Biodiesel is considered as a renewable hydrogen source for solid oxide fuel cells (SOFCs). This study contributes to a fundamental understanding of biodiesel autothermal reforming (ATR), which has not yet been widely explored in the open literature. Ultra-low sulfur diesel (ULSD) ATR is established as a baseline for this analysis. This work applies a micro-soot meter based on a photo-acoustic method to quantify the condensed carbon from a single-tube reactor, and uses a mass spectrometer to measure the effluent gas composition under different operating conditions (reformer temperature, steam/carbon ratio, oxygen/carbon ratio, and gas hourly space velocity). The key objective is to identify the optimum operating environment for biodiesel ATR with carbon-free deposition and peak hydrogen yield. Thermodynamic analysis based on the method of total Gibbs free energy minimization is used to evaluate the equilibrium composition of effluent from the reformer. The experimental investigations complimented with this theoretical analysis of biodiesel ATR enable effectively optimizing the onboard reforming conditions. This study is one component of a three-part investigation of bio-fuel reforming, also including fuel vaporization and reactant mixing (Part 1) and biodiesel–diesel blends (Part 3).