Renewable Hydrogen Production Research Articles

The application of perovskite materials in solar water splitting

Solar water splitting is a promising strategy for sustainable production of renewable hydrogen, and solving the crisis of energy and environment in the world. However, large-scale application of this method is hampered by the efficiency and the expense of the solar water splitting systems. Searching for non-toxic, low-cost, efficient and stable photocatalysts is an important way for solar water splitting. Due to the simplicity of structure and the flexibility of composition, perovskite based photocatalysts have recently attracted widespread attention for application in solar water splitting. In this review, the recent developments of perovskite based photocatalysts for water splitting are summarized. An introduction including the structures and properties of perovskite materials, and the fundamentals of solar water splitting is first provided. Then, it specifically focuses on the strategies for designing and modulating perovskite materials to improve their photocatalytic performance for solar water splitting. The current challenges and perspectives of perovskite materials in solar water splitting are also reviewed. The aim of this review is to summarize recent findings and developments of perovskite based photocatalysts and provide some useful guidance for the future research on the design and development of highly efficient perovskite based photocatalysts and the relevant systems for water splitting.

Nonprecious metal's graphene‐supported electrocatalysts for hydrogen evolution reaction: Fundamentals to applications

AbstractSustainable production of hydrogen is a hopeful requirement of a strategic future economy and development. Water splitting driven by electricity is a favorable pathway for renewable hydrogen production. This critical review highlighted recent efforts toward the development of the nanoscale synthesis of nonprecious metal's graphene‐supported electrocatalysts and their electrocatalytic features for remarkable hydrogen evolution reaction (HER). Different essential nonprecious metal's graphene‐supported electrocatalysts, including metal carbides, sulfides, phosphides, selenides, oxides, and nitrides are reviewed. In the exploration, attention is given to the strategies of activity enhancement, the synthetic approach, and the composition/structure electrocatalytic‐performance relationship of these HER electrocatalysts. We are hopeful that this review confers a new momentum to the rational design of remarkable performance nonprecious metal's graphene‐supported electrocatalysts and comprehensive guide for researchers to utilize the subject catalysts in regular water splitting.

Effect of support size for stimulating hydrogen production in phenol steam reforming using Ni-embedded TiO2 nanocatalyst

Fabrication of reducible titanium dioxide (TiO2) loaded with nickel (Ni) to maximize metal-support interaction for stimulating hydrogen (H2) production via phenol steam reforming (PSR) has been investigated. Catalysts, synthesized by sol-gel assisted impregnation method, were characterized by XRD, FE-SEM, EDX, BET, H2-TPR and TEM techniques. The effects of three different catalyst sizes namely Ni/TiO2-A (11−49 nm), Ni/TiO2-B (22−196 nm) and Ni/TiO2-C (69−205 nm) for their mass transfer limitation, catalytic activity and coke formations were evaluated. Using smaller particle sizes of TiO2 higher BET surface area with good morphology and Ni dispersion was achieved. The Ni/TiO2-A sample shows highest phenol reforming activity with phenol conversion and H2 yield of 98.3 and 76.9 %, respectively. When large sizes TiO2 particles in Ni/TiO2-B and Ni/TiO2-C samples were employed, phenol conversion of 93.7 and 73.1 % and H2 yield of 71.2 and 55.6%, respectively, were achieved. This reveals that smaller support particle sizes have higher conversion and yields, and activity was declined when support size was increased to larger particle sizes. This was obviously small particle sizes resulted in larger surface area, higher metal dispersion and efficient surface reactions with minimum internal diffusion effects. Furthermore, stability analysis reveals continuous H2 production over smaller particles without obvious deactivation, however, activity was declined over time on stream using large support size due to obvious coke depositions. Thus, supports sizes and interaction of metal and support has significant contribution to maximize activity and stability and can be further employed in reforming systems for renewable hydrogen production.

Hydrogen Production from Steam Reforming of Acetic Acid as a Model Compound of the Aqueous Fraction of Microalgae HTL Using Co-M/SBA-15 (M: Cu, Ag, Ce, Cr) Catalysts

Hydrogen production derived from thermochemical processing of biomass is becoming an interesting alternative to conventional routes using fossil fuels. In this sense, steam reforming of the aqueous fraction of microalgae hydrothermal liquefaction (HTL) is a promising option for renewable hydrogen production. Since the HTL aqueous fraction is a complex mixture, acetic acid has been chosen as model compound. This work studies the modification of Co/SBA-15 catalyst incorporating a second metal leading to Co-M/SBA-15 (M: Cu, Ag, Ce and Cr). All catalysts were characterized by N2 physisorption, ICP-AES, XRD, TEM, H2-TPR, H2-TPD and Raman spectroscopy. The characterization results evidenced that Cu and Ag incorporation decreased the cobalt oxides reduction temperatures, while Cr addition led to smaller Co0 crystallites better dispersed on the support. Catalytic tests done at 600 °C, showed that Co-Cr/SBA-15 sample gave hydrogen selectivity values above 70 mol % with a significant reduction in coke deposition.

Renewable Methanol Synthesis

AbstractRenewable methanol production is an emerging technology that bridges the gap in the shift from fossil fuel to renewable energy. Two thirds of the global emission of CO2 stems from humanity's increasing energy need from fossil fuels. Renewable energy, mainly from solar and wind energy, suffers from supply intermittency, which current grid infrastructures cannot accommodate. Excess renewable energy can be harnessed to power the electrolysis of water to produce hydrogen, which can be used in the catalytic hydrogenation of waste CO2 to produce renewable methanol. This review considers methanol production in the current context, regionally for Europe, which is dominated by Germany, and globally by China. Appropriate carbon‐based feedstock for renewable methanol production is considered, as well as state‐of‐the‐art renewable hydrogen production technologies. The economics of renewable methanol production necessitates the consideration of regionally relevant methanol derivatives. The thermodynamics, kinetics, catalytic reaction mechanism, operating conditions and reactor design are reviewed in the context of renewable methanol production to reveal the most up to date understanding.

Triplet-Triplet Annihilation Upconversion for Photocatalytic Hydrogen Evolution.

The solar generation of hydrogen by water splitting provides a promising path for renewable hydrogen production and solar energy storage. Upconversion of low-energy photons into high-energy photons constitutes a promising strategy to enhance the light harvesting efficiency of artificial hydrogen production systems. In the present study, upconversion micelles are integrated with Cd0.5 Zn0.5 S to construct solar energy conversion systems. The upconversion micelle is employed to upconvert red photons to cyan photons. Cd0.5 Zn0.5 S is sensitized by upconverted cyan light to produce hydrogen, but not by incident red light without triplet-triplet annihilation upconversion (TTA-UC). The performance of the upconversion photocatalytic system was dramatically affected by the concentration of Cd0.5 Zn0.5 S and the irradiation intensity. This novel system was able to produce about 2.3 μL hydrogen after 5 h of red light (629 nm) irradiation (2.4 mW cm-2 ). The present study provides a candidate for applications using low-energy photons for solar hydrogen generation.

A Short Overview on the Hydrogen Production Via Aqueous Phase Reforming (APR) of Cellulose, C6-C5 Sugars and Polyols

The use of lignocellulosic biomasses for the production of renewable hydrogen is surely among the hot-topic research tasks. In this review, we report on the recent advances in the catalytic conversion of cellulose and its derived C6-C5 sugars (glucose, fructose, and xylose) and polyols (sorbitol and xylitol) into hydrogen via aqueous phase reforming (APR) reactions. The APR processes are considered to be new sustainable catalytic routes for converting the carbohydrate fraction of biomasses into hydrogen at milder reaction conditions if compared with the traditional reforming reactions. Particular emphasis is given to the development of new and active catalysts and to the optimization of reaction conditions that aimed to maximize hydrogen production with a low concentration of CO avoiding, at the same time, the formation of alkanes.

Metal Boride‐Based Catalysts for Electrochemical Water‐Splitting: A Review

AbstractElectrocatalytic water‐splitting has gained a firm hold in the area of renewable hydrogen production owing to its integrative compatibility with intermittent energy sources. However, wide‐scale implementation of this technology demands discovery of new electrode materials that strike a good balance between efficiency, stability, and cost. In the pool of inexpensive electrodes capable of catalyzing hydrogen and oxygen evolution reactions, metal borides/borates have made a big splash in the last decade. However, the research in this family of electrocatalysts remains unorganized owing to the diversity of reports. This review summarizes the past and present research progress in metal borides/borates for electrocatalytic water‐splitting. The fundamental reasons for electrochemical behavior in different metal borides/borates are highlighted here, also including some comments regarding erroneous practices in the performance evaluation of metal borides/borates. Various strategies used to enhance the electrocatalytic performance of metal borides/borates are discussed in detail. Different methods evolved over the years for the synthesis of metal borides/borates are also discussed. Finally, an assessment of the commercial viability of metal borides/borates is made and future research directions are suggested.

Heterostructured Ni(OH)2/Ni3S2 Supported on Ni Foam as Highly Efficient and Durable Bifunctional Electrodes for Overall Water Electrolysis

Development of efficient, stable, and robust bifunctional electrodes is important for the practical and industrial application of water electrolysis technologies for renewable hydrogen production. ...

Renewable hydrogen production by steam reforming of butanol over multiwalled carbon nanotube-supported catalysts

The conversion of bio-oxygenates into hydrogen (H2) via catalytic steam reforming is a green approach for H2 generation. In the present work, butanol was chosen as renewable feedstock for producing H2. Two catalysts supported on multiwalled carbon nanotubes, Ni/CNT and Co/CNT, were synthesized by the wetness impregnation method and used for butanol reforming. Trials were performed in a fixed-bed reactor in the 623–773 K range using S/C ratio equal to 33.3 mol/mol (here, S/C denotes steam to carbon ratio). The Ni/CNT catalyst exhibited higher reforming activity. The best catalytic performance for Ni/CNT was observed at T = 773 K. At this temperature, high values of butanol conversion (87.3%) and H2 yield (0.75 mol/mol) were observed at W/FA0 = 16.7 g h/mol (here, W is the catalyst mass and FA0 is the molar flow rate of butanol at the inlet). The performance of Ni/CNT catalyst for steam reforming of synthetic bio-butanol was also investigated at T = 773 K and H2 yield of 0.65 mol/mol was achieved.

Review of renewable energy-based hydrogen production processes for sustainable energy innovation

In this review, we primarily analyze the hydrogen production technologies based on water and biomass, including the economic, technological, and environmental impacts of different types of hydrogen production technologies based on these materials, and comprehensively compare them. Our analyses indicate that all renewable energy-based approaches for hydrogen production are more environmentally friendly than fossil-based hydrogen generation approaches. However, the technical ease and economic efficiency of hydrogen production from renewable sources of energy needs to be further improved in order to be applied on a large scale. Compared with other renewable energy-based methods, hydrogen production via biomass electrolysis has several advantages, including the ease of directly using raw biomass. Furthermore, its environmental impact is smaller than other approaches. Moreover, using a noble metal, catalyst-free anode for this approach can ensure a considerably low power consumption, which makes it a promising candidate for clean and efficient hydrogen production in the future.

Assessment of sustainable high temperature hydrogen production technologies

Apart from being a major feedstock for chemical production, hydrogen is also a very promising energy carrier for the future energy. Currently hydrogen is predominantly produced via fossil routes, but as green energy sources are gaining a larger role in the energy mix, novel and green production routes are emerging. The most abundant renewable hydrogen sources are water and biomass, which allow several possible processing routes, such as electrolysis, thermochemical cycles and gasification. By introducing heat to the process the required electricity demand can be reduced (high temperature electrolysis) or practically eliminated (thermochemical cycles). Each renewable hydrogen production route has its own strength and weaknesses; the choice of the most suitable method is always dependent on the economical potentials and the location. The aim of this paper is to evaluate the different high temperature, renewable hydrogen production technologies.

Modeling & optimization of renewable hydrogen production from biomass via anaerobic digestion & dry reformation

There is a growing interest in the usage of hydrogen as an environmentally cleaner form of energy for end users. However, hydrogen does not occur naturally and needs to be produced through energy intensive processes, such as steam reformation. In order to be truly renewable, hydrogen must be produced through processes that do not lead to direct or indirect carbon dioxide emissions. Dry reformation of methane is a route that consumes carbon dioxide to produce hydrogen. This work describes the production of hydrogen from biomass via anaerobic digestion of waste biomass and dry reformation of biogas. This process consumes carbon dioxide instead of releasing it and uses only renewable feed materials for hydrogen production. An end-to-end simulation of this process is developed primarily using Aspen HYSYS® and consists of steady state models for anaerobic digestion of biomass, dry reformation of biogas in a fixed-bed catalytic reactor containing Ni–Co/Al2O3 catalyst, and a custom-model for hydrogen separation using a hollow fibre membrane separator. A mixture-process variable design is used to simultaneously optimize feed composition and process conditions for the process. It is identified that if biogas containing 52 mol% methane, 38 mol% carbon dioxide, and 10 mol% water (or steam) is used for hydrogen production by dry reformation at a temperature of 837.5 °C and a pressure of 101.3 kPa; optimal values of 89.9% methane conversion, 99.99% carbon dioxide conversion and hydrogen selectivity 1.21 can be obtained.

Renewable electrolytic hydrogen potential in Algeria

The present paper deals with the assessment of the renewable hydrogen production potential in Algeria. The studied system produces hydrogen by electrolysis of water; electricity is supplied by a photovoltaic generator. Adequate mathematical models were used to calculate the electrolytic hydrogen production. Detailed hourly simulations were used to assess the potential for the entire country and to draw it maps. Throughout this study, the influence of the tilt angle of a photovoltaic generator has been investigated. It has been observed that the tilt angle has an impact on solar energy received by the photovoltaic generator, the produced solar electrical power and the rate of hydrogen production. We have calculated the optimal angles to maximize each element. We were particularly interested in the optimal angle to maximize hydrogen production. We found that the solar hydrogen potential for Algeria varies from 0.10 Nm3/m2/d to 0.14 Nm3/m2/d. This potential is quite significant, especially in the arid region of southeastern Algeria. The lowest potential is located in the northeast region. For stand-alone systems, it is important to assess the minimum available level, as their sizing takes into account the most unfavorable case. This level is between 0.07 Nm3/m2/d and 0.13 Nm3/m2/d. This shows that, even for a stand-alone system, the potential is quite high. Finally, we provide robust correlations that allow calculating the potential and the angle of inclination maximizing it for the whole of Algeria.

A study on the efficacy of noble metal catalysts for butanol steam reforming

Biomass-derived oxygenates such as biobutanol are potential candidates for renewable hydrogen (H2) production. In this work, the model compound butanol was chosen as feed for H2 production. Steam reforming of butanol was investigated at mild temperatures (623–773 K) over two noble metal catalysts Pt/Al2O3 and Pd/Al2O3 renowned for their reforming activity. Trials were performed in a fixed-bed reactor using 1–4 wt% butanol solutions as feedstock. At T = 773 K and W/FA0 = 166.8 g h/mol (here, W and FA0 denote mass of catalyst and molar flow rate of butanol in the feed), butanol conversion was almost complete over both catalysts. However, turnover frequency observed over Pt/Al2O3 (TOFH2 = 45.5 min−1) was higher than that achieved using Pd/Al2O3 (TOFH2 = 21.3 min−1). The apparent energy of activation for the disappearance of butanol over Pt/Al2O3 and Pd/Al2O3 was found to be 22.9 and 30.2 kJ/mol respectively. Thus, this work has provided key insights into H2 production from butanol using noble metals at mild reaction conditions.

(Invited) Emerging Chalcopyrite Photo-absorbers for Renewable Hydrogen Production

Photoelectrochemical (PEC) water splitting is an attractive method for efficient renewable hydrogen production. However, the cost, efficiency and durability of lab-scale systems are not yet at the level required to make this technology economically attractive. Amongst all materials studied to date, the chalcopyrite class is arguably one of the most promising classes for PEC water splitting, as it has already demonstrated low-cost and high photoconversion capabilities as a photovoltaic material. In the context of PEC, our group has shown that co-evaporated 1.65 eV bandgap (EG) CuGaSe2 is capable of evolving hydrogen with Faradaic efficiency greater than 85% and generate photocurrent densities over 15 mA.cm-­2, as measured in a 3-electrode configuration in 0.5M H2SO4 under simulated AM1.5G illumination. Unfortunately, CuGaSe2’s narrow EG limits its integration as top absorber into a dual junction stacked PEC device (also known as hybrid photoelectrode, HPE). In the present communication, we report on our latest efforts to synthesize wide-EG (1.8-2.0 eV) chalcopyrites, compatible with the HPE integration scheme, and capable of generating saturated photocurrent densities greater than 10 mA/cm2. We present specifically results on EG tunable Cu(In,Ga)S2, CuGa(S,Se)2 and CuGa3Se5. We also discuss some of the strategies developed to improve their surface energetics for the hydrogen evolution reaction, including the use of non toxic n-type buffer layers. We also include recent durability testing of chalcopyrite photocathodes coated with metal oxide protection layers. Finally, we present solid-state techniques and theoretical modeling used by our team to identify possible pitfalls in these material systems and discuss potential paths for improvement.

(Invited) Toward Highly Efficient Solar Water Splitting: A Concurrent Electrical, Optical, and Catalytic Design

Energy crisis is a broad and complex global topic. Natural resources such as gas and oil are in limited in supply. Development towards renewable resources is one of the most important technologies in the world. Currently, photocatalytic and photoelectrochemical (PEC) water splitting devices under the irradiation of sunlight have received much attention for the production of renewable hydrogen from water. Solar energy conversion and storage through photoelectrolysis of water using semiconductors as both light absorber and energy converter to store solar energy in simple chemical bond, H2, become highly desirable approaches to solving the energy shortage challenge. We focus on the effort to develop an efficient Si-based PEC water splitting device. We introduce the surface textured Si heterojunction PEC cell consisting of ultrathin amorphous Si/crystalline Si as efficient and robust photoelectrodes. The solar to hydrogen conversion efficiency has been improved to 13.26%, which is the highest ever reported for Si-based photocathodes. Later on, we design the cascading energy band structure in Si via doping for facilitating carrier separation and novel electrode structures for 360° light harvesting for hydrogen generation with ultrahigh current densities of 61.2 mAcm-2. The cells have been further demonstrated with excellent hydrogen production rate. In addition, our method can significantly improve the stability of Si-based solar cells in water to sustain up to 300 hr. These multifunctional designs provide the potential for the future development in the renewable energy market.

Hydrogen from Renewables: A Case Study of Glycerol Reforming

Biomass is an interesting candidate raw material for the production of renewable hydrogen. The conversion of biomass into hydrogen can be achieved by several processes. In particular, this short review focuses on the recent advances in glycerol reforming to hydrogen, highlighting the development of new and active catalysts, the optimization of reaction conditions, and the use of non-innocent supports as advanced materials for supported catalysts. Different processes for hydrogen production from glycerol, especially aqueous phase reforming (APR) and steam reforming (SR), are described in brief. Thermodynamic analyses, which enable comparison with experimental studies, are also considered. In addition, research advances in terms of life cycle perspective applied to support R&D activities in the synthesis of renewable H2 from biomass are presented. Lastly, also featured is an evaluation of the studies published, as evidence of the increased interest of both academic research and the industrial community in biomass conversion to energy sources.

Recent advances in renewable hydrogen production by thermo-catalytic conversion of biomass-derived glycerol: Overview of prospects and challenges

Glycerol is the main by-products obtained from the transesterification of vegetable oils and animal fats to produce biodiesel which is an important biofuel used for transportation. The increase in the global energy demand has pushed up the production of biodiesel with a corresponding increase in glycerol production over the years. The thermo-catalytic process is gaining wide popularity as sustainable technical routes of converting glycerol to renewable hydrogen. There exists a great potential of utilizing hydrogen as a critical part of a more sustainable and secure energy mix. Hence, this study focusses on the review of the recent advances and development in the thermo-catalytic conversion of glycerol to renewable hydrogen in the last one decade. The analysis of the reviewed articles showed that substantial efforts had been made in the application of thermo-catalytic process for the conversion of glycerol to renewable hydrogen. Glycerol reforming using steam, carbon dioxide (CO2) and oxygen (O2) have received significant research attention and have been found to have great potential as technological routes for hydrogen production. Whereas, the use of the photocatalytic glycerol reforming has the advantages of energy-saving by utilizing the vast available solar resources and suitable photocatalysts. However, each of the thermo-catalytic processes exhibits inherent challenges which have been a bottleneck to the development of the process to industrial scales. Nevertheless, the prospect of employing each of the thermo-catalytic processes for hydrogen production via glycerol conversion was identified with the possible suggestion of strategies of overcoming the challenges.

Catalytic Steam Reforming of Toluene for Hydrogen Production over Nickel-Cobalt Supported Activated Carbon

Hydrogen may play a key role in future sustainable energy system as a carrier of renewable energy to replace the conventional fossil fuel. Biomass gasification is the most promising method in renewable hydrogen production technologies. However, the tar by-product poses great obstacle in the realization of commercial biomass gasification. In this work, the performance of Ni and/or Co supported on modified-palm kernel shell-derived activated carbon (AC) catalyst in steam reforming of toluene (SRT) for the production of hydrogen has been investigated. Toluene has been chosen as a model compound since it represents one of the major tar compositions. The effects of nitric acid in the surface pretreatment of AC (ACN) and the influence of Ni and/or Co loading on the catalyst support are studied. The catalysts are characterized using FTIR, BET, XRD, TGA and FESEM-EDX. The modified-AC support shows that the surface area, microporous structure and surface oxygenated functional group (SOFG) increase, leading to a homogeneous distribution of metal particles. The highest toluene conversion (Xtoluene) and hydrogen yield (YH2) obtained over 10%Ni-10%Co/ACN are 70% and 69%, respectively. The catalytic performance of bimetallic Ni–Co/ACN catalyst is more significant compared to monometallic Ni- and Co-supported catalysts. The highest catalytic performance achieved can be attributed to the larger surface area and unique porous structure of the modified-AC support as well as the formation of Ni–Co solid solution alloys that improve its coke-resistant capability with low carbon formation during SRT. The modified palm kernel shell AC-supported bimetal catalyst has high potential as a biomass-based catalyst for the applications in biomass tar removal toward hydrogen production due to its good coke-resistance properties.