Production & Supply Chain
The Use of Strontium Ferrite in Chemical Looping Systems
May 2020
Publication
This work reports a detailed chemical looping investigation of strontium ferrite (SrFeO3−δ) a material with the perovskite structure type able to donate oxygen and stay in a nonstoichiometric form over a broad range of oxygen partial pressures starting at temperatures as low as 250°C (reduction in CO measured in TGA). SrFeO3−δ is an economically attractive simple but remarkably stable material that can withstand repeated phase transitions during redox cycling. Mechanical mixing and calcination of iron oxide and strontium carbonate was evaluated as an effective way to obtain pure SrFeO3−δ. In–situ XRD was performed to analyse structure transformations during reduction and reoxidation. Our work reports that much deeper reduction from SrFeO3−δ to SrO and Fe is reversible and results in oxygen release at a chemical potential suitable for hydrogen production. Thermogravimetric experiments with different gas compositions were applied to characterize the material and evaluate its available oxygen capacity. In both TGA and in-situ XRD experiments the material was reduced below δ=0.5 followed by reoxidation either with CO2 or air to study phase segregation and reversibility of crystal structure transitions. As revealed by in-situ XRD even deeply reduced material regenerates at 900°C to SrFeO3−δ with a cubic structure. To investigate the catalytic behaviour of SrFeO3−δ in methane combustion experiments were performed in a fluidized bed rig. These showed SrFeO3−δ donates O2 into the gas phase but also assists with CH4 combustion by supplying lattice oxygen. To test the material for combustion and hydrogen production long cycling experiments in a fluidized bed rig were also performed. SrFeO3−δ showed stability over 30 redox cycles both in experiments with a 2-step oxidation performed in CO2 followed by air as well as a single step oxidation in CO2 alone. Finally the influence of CO/CO2 mixtures on material performance was tested; a fast and deep reduction in elevated pCO2 makes the material susceptible to carbonation but the process can be reversed by increasing the temperature or lowering pCO2.
Computational Intelligence Approach for Modeling Hydrogen Production: A Review
Mar 2018
Publication
Hydrogen is a clean energy source with a relatively low pollution footprint. However hydrogen does not exist in nature as a separate element but only in compound forms. Hydrogen is produced through a process that dissociates it from its compounds. Several methods are used for hydrogen production which first of all differ in the energy used in this process. Investigating the viability and exact applicability of a method in a specific context requires accurate knowledge of the parameters involved in the method and the interaction between these parameters. This can be done using top-down models relying on complex mathematically driven equations. However with the raise of computational intelligence (CI) and machine learning techniques researchers in hydrology have increasingly been using these methods for this complex task and report promising results. The contribution of this study is to investigate the state of the art CI methods employed in hydrogen production and to identify the CI method(s) that perform better in the prediction assessment and optimization tasks related to different types of Hydrogen production methods. The resulting analysis provides in-depth insight into the different hydrogen production methods modeling technique and the obtained results from various scenarios integrating them within the framework of a common discussion and evaluation paper. The identified methods were benchmarked by a qualitative analysis of the accuracy of CI in modeling hydrogen production providing extensive overview of its usage to empower renewable energy utilization.
Seasonal Storage and Alternative Carriers: A Flexible Hydrogen Supply Chain Model
May 2017
Publication
A viable hydrogen infrastructure is one of the main challenges for fuel cells in mobile applications. Several studies have investigated the most cost-efficient hydrogen supply chain structure with a focus on hydrogen transportation. However supply chain models based on hydrogen produced by electrolysis require additional seasonal hydrogen storage capacity to close the gap between fluctuation in renewable generation from surplus electricity and fuelling station demand. To address this issue we developed a model that draws on and extends approaches in the literature with respect to long-term storage. Thus we analyse Liquid Organic Hydrogen Carriers (LOHC) and show their potential impact on future hydrogen mobility. We demonstrate that LOHC-based pathways are highly promising especially for smaller-scale hydrogen demand and if storage in salt caverns remains uncompetitive but emit more greenhouse gases (GHG) than other gaseous or hydrogen ones. Liquid hydrogen as a seasonal storage medium offers no advantage compared to LOHC or cavern storage since lower electricity prices for flexible operation cannot balance the investment costs of liquefaction plants. A well-to-wheel analysis indicates that all investigated pathways have less than 30% GHG-emissions compared to conventional fossil fuel pathways within a European framework.
Production Costs for Synthetic Methane in 2030 and 2050 of an Optimized Power-to-Gas Plant with Intermediate Hydrogen Storage
Aug 2019
Publication
The publication gives an overview of the production costs of synthetic methane in a Power-to-Gas process. The production costs depend in particularly on the electricity price and the full load hours of the plant sub-systems electrolysis and methanation. The full-load hours of electrolysis are given by the electricity supply concept. In order to increase the full-load hours of methanation the size of the intermediate hydrogen storage tank and the size of the methanation are optimised on the basis of the availability of hydrogen. The calculation of the production costs for synthetic methane are done with economics for 2030 and 2050 and the expenditures are calculated for one year of operation. The sources of volume of purchased electricity are the short-term market long-term contracts direct-coupled renewable energy sources or seasonal use of surpluses. Gas sales are either traded on the short-term market or guaranteed by long-term contracts. The calculations show that an intermediate storage tank for hydrogen adjustment of the methanation size and operating electrolysis and methanation separately increase the workload of the sub-system methanation. The gas production costs can be significantly reduced. With the future expected development of capital expenditures operational expenditure electricity prices gas costs and efficiencies an economic production of synthetic natural gas for the years 2030 especially for 2050 is feasible. The results show that Power-to-Gas is an option for long-term large-scale seasonal storage of renewable energy. Especially the cases with high operating hours for the sub-system methanation and low electricity prices show gas production costs below the expected market prices for synthetic gas and biogas.
Aqueous Phase Reforming of the Residual Waters Derived from Lignin-rich Hydrothermal Liquefaction: Investigation of Representative Organic Compounds and Actual Biorefinery Streams
Sep 2019
Publication
Secondary streams in biorefineries need to be valorized to improve the economic and environmental sustainability of the plants. Representative model compounds of the water fraction from the hydrothermal liquefaction (HTL) of biomass were subjected to aqueous phase reforming (APR) to produce hydrogen. Carboxylic and bicarboxylic acids hydroxyacids alcohols cycloketones and aromatics were identified as model compounds and tested for APR. The tests were performed with a Pt/C catalyst and the influence of the carbon concentration (0.3–1.8 wt. C%) was investigated. Typically the increase of the concentration negatively affected the conversion of the feed toward gaseous products without influencing the selectivity toward hydrogen production. A synthetic ternary mixture (glycolic acid acetic acid lactic acid) was subjected to APR to evaluate any differences in performance compared to the tests with single compounds. Indeed glycolic acid reacted faster in the mixture than in the corresponding single compound test while acetic acid remained almost unconverted. The influence of the reaction time temperature and carbon concentration was also evaluated. Finally residual water resulting from the HTL of a lignin-rich stream originating from an industrial-scale lignocellulosic ethanol process was tested for the first time after a thorough characterization. In this framework the stability of the catalyst was studied and found to be correlated to the presence of aromatics in the aqueous feedstock. For this reason the influence of an extraction procedure for the selective removal of these compounds was explored leading to an improvement in the APR performance.
Thermodynamic Assessment of the Novel Concept of the Energy Storage System Using Compressed Carbon Dioxide, Methanation and Hydrogen Generator
Jul 2021
Publication
The main aim of this paper is to characterize the concept of a novel energy storage system based on compressed CO2 storage installation that uses an infrastructure of depleted coal mines to provide required volume of tanks and additionally hydrogen generators and a methanation installation to generate synthetic natural gas that can be used within the system or taken out of it e.g. to a gas grid. A detailed mathematical model of the proposed solution was built using own codes and Aspen Plus software. Thermodynamic evaluation aiming at determining parameters composition and streams in all the most important nodes of the system for the nominal point and when changing a defined decision variable δ (in the range from 0.1 to 0.9) was made. The evaluation was made based on the storage efficiency volume of the tanks and flows of energy within the system. The storage efficiency in the nominal point reached 45.08% but was changing in the range from 35.06% (for δ = 0.1) to 63.93% (for δ = 0.9). For the nominal value of δ equal to 0.5 volume of the low-pressure tank (LPT) was equal to 132869 m3 while of the high pressure tank (HPT) to 1219 m3 . When changing δ these volumes were changing from 101900 m3 to 190878 m3 (for LPT) and from 935 to 1751 m3 (for HPT) respectively. Detailed results are presented in the paper and indicate high storage potential of the proposed solution in regions with underground mine infrastructure.
Hydrothermal Conversion of Lignin and Black Liquor for Phenolics with the Aids of Alkali and Hydrogen Donor
Jun 2019
Publication
The potentials of phenolic productions from lignin and black liquor (BL) via hydrothermal technology with the aids of alkalis and hydrogen donors were investigated by conducting batch experiments in micro-tube reactors with 300 °C sub-critical water as the solvent. The results showed that all the employed alkalis improved lignin degradation and thus phenolics production and the strong alkalis additionally manifested deoxygenation to produce more phenolics free of methoxyl group(s). Relatively hydrogen donors more visibly facilitated phenolics formation. Combination of strong alkali and hydrogen donors exhibited synergistically positive effects on producing phenolics (their total yield reaching 22 wt%) with high selectivities to phenolics among which the yields of catechol and cresols respectively peaked 16 and 3.5 wt%. BL could be hydrothermally converted into phenolics at high yields (approaching 10 wt% with the yields of catechol and cresols of about 4 and 2 wt% respectively) with the aids of its inherent alkali and hydrogen donors justifying its cascade utilization.
Transient Numerical Modeling and Model Predictive Control of an Industrial-scale Steam Methane Reforming Reactor
Mar 2021
Publication
A steam methane reforming reactor is a key equipment in hydrogen production and numerical analysis and process control can provide a critical insight into its reforming mechanisms and flexible operation in real engineering applications. The present paper firstly studies the transport phenomena in an industrial-scale steam methane reforming reactor by transient numerical simulations. Wall effect and local non thermal equilibrium is considered in the simulations. A temperature profile of the tube outer wall is given by user defined functions integrated into the ANSYS FLUENT software. Dynamic simulations show that the species distribution is closely related to the temperature distribution which makes the temperature of the reactor tube wall an important factor for the hydrogen production of the reformer and the thermal conductivity of the catalyst network is crucial in the heat transfer in the reactor. Besides there exists a delay of the reformer's hydrogen production when the temperature profile of the tube wall changes. Among inlet temperature inlet mass flow rate and inlet steam-to-carbon (S/C) ratio the mass flow rate is the most influencing factor for the hydrogen production. The dynamic matrix control (DMC) scheme is subsequently designed to manipulate the mole fraction of hydrogen of the outlet to the target value by setting the temperature profile trajectory of the reforming tube with time. The proportional-integral control strategy is also studied for comparison. The closed-loop simulation results show that the proposed DMC control strategy can reduce the overshoot and have a small change of the input variable. In addition the disturbances of feed disturbance can also be well rejected to assure the tracking performance indicating the superiority of the DMC controller. All the results give insight to the theoretical analysis and controller design of a steam methane reformer and demonstrate the potential of the CFD modeling in study the transport mechanism and the idea of combining CFD modelling with controller design for the real application.
Flexible Power & Biomass-to-Methanol Plants: Design Optimization and Economic Viability of the Electrolysis Integration
Nov 2021
Publication
This paper assesses the optimal design criteria of a flexible power and biomass to methanol (PBtM) plant conceived to operate both without green hydrogen addition (baseline mode) and with hydrogen addition (enhanced mode) following an intermittent use of the electrolysis system which is turned on when the electricity price allows an economically viable hydrogen production. The assessed plant includes a gasification section syngas cleaning and compression methanol synthesis and purification and heat recovery steam cycle to be flexibly operated. A sorption-enhanced gasification technology allows to produce a tailored syngas for the downstream synthesis in both the baseline and enhanced operating conditions by controlling the in-situ CO2 separation rate. Two designs are assessed for the methanol synthesis unit with two different reactor sizes: (i) a larger reactor designed on the enhanced operation mode (enhanced reactor design – ERD) and (ii) a smaller reactor designed on the baseline operation mode (baseline reactor design – BRD). The ERD design resulted to be preferable from the techno economic perspectives resulting in 20% lower cost of the e-MeOH (30.80 vs. 37.76 €/ GJLHV) with the baseline assumptions (i.e. 80% of electrolyzer capacity factor and 2019 Denmark day-ahead market electricity price). Other important outcomes are: (i) high electrolysis capacity factor is needed to obtain competitive cost of e-MeOH and (ii) advantages of flexibly operated PBtM plants with respect to inflexible PBtM plants are significant in scenarios with high penetration of intermittent renewables leading to low average prices of electricity but also longer periods of high peak prices.
True Cost of Solar Hydrogen
Sep 2021
Publication
Green hydrogen will be an essential part of the future 100% sustainable energy and industry system. Up to one-third of the required solar and wind electricity would eventually be used for water electrolysis to produce hydrogen increasing the cumulative electrolyzer capacity to about 17 TWel by 2050. The key method applied in this research is a learning curve approach for the key technologies i.e. solar photovoltaics (PV) and water electrolyzers and levelized cost of hydrogen (LCOH). Sensitivities for the hydrogen demand and various input parameters are considered. Electrolyzer capital expenditure (CAPEX) for a large utility-scale system is expected to decrease from the current 400 €/kWel to 240 €/kWel by 2030 and to 80 €/kWel by 2050. With the continuing solar PV cost decrease this will lead to an LCOH decrease from the current 31–81 €/ MWhH2LHV (1.0–2.7 €/kgH2) to 20–54 €/MWhH2LHV (0.7–1.8 €/kgH2) by 2030 and 10–27 €/MWhH2LHV (0.3–0.9 €/kgH2) by 2050 depending on the location. The share of PV electricity cost in the LCOH will increase from the current 63% to 74% by 2050.
HydroGenerally - Episode 1: The Colours of Hydrogen
Mar 2022
Publication
This first episode was inspired by an Innovate UK KTN perspective commenting on the UK government’s Hydrogen Strategy released by the Department of Business Energy and Industrial Strategy (BEIS) in August 2021. Following the publication of this perspective it was very evident to our Innovate UK KTN experts that the uses and challenges of ‘blue’ and ‘green’ hydrogens were generating a strong debate depending on their application areas.
Over a 20-minute discussion Simon Steffan and Sam try to answer the questions: how is hydrogen currently produced? How will it be produced in the future? And how will it fit in with the energy system?
The podcast can be found on their website
Over a 20-minute discussion Simon Steffan and Sam try to answer the questions: how is hydrogen currently produced? How will it be produced in the future? And how will it fit in with the energy system?
The podcast can be found on their website
Hydrogen Production from the Air
Sep 2022
Publication
Green hydrogen produced by water splitting using renewable energy is the most promising energy carrier of the low-carbon economy. However the geographic mismatch between renewables distribution and freshwater availability poses a significant challenge to its production. Here we demonstrate a method of direct hydrogen production from the air namely in situ capture of freshwater from the atmosphere using hygroscopic electrolyte and electrolysis powered by solar or wind with a current density up to 574 mA cm−2 . A prototype of such has been established and operated for 12 consecutive days with a stable performance at a Faradaic efficiency around 95%. This so-called direct air electrolysis (DAE) module can work under a bone-dry environment with a relative humidity of 4% overcoming water supply issues and producing green hydrogen sustainably with minimal impact to the environment. The DAE modules can be easily scaled to provide hydrogen to remote (semi-) arid and scattered areas.
Energy Efficiency Based Control Strategy of a Three-Level Interleaved DC-DC Buck Converter Supplying a Proton Exchange Membrane Electrolyzer
Aug 2019
Publication
To face the intensive use of natural gas and other fossil fuels to generate hydrogen water electrolysis based on renewable energy sources (RES) seems to be a viable solution. Due to their fast response times and high efficiency proton exchange membrane electrolyzer (PEM EL) is the most suitable technology for long-term energy storage combined with RES. Like fuel cells the development of fit DC-DC converters is mandatory to interface the EL to the DC grid. Given that PEM EL operating voltages are quite low and to meet requirements in terms of output current ripples new emerging interleaved DC-DC converter topologies seem to be the best candidates. In this work a three-level interleaved DC-DC buck converter has been chosen to supply a PEM EL from a DC grid. Therefore the main objective of this paper is to develop a suitable control strategy of this interleaved topology connected to a PEM EL emulator. To design the control strategy investigations have been carried out on energy efficiency hydrogen flow rate and specific energy consumption. The obtained experimental results validate the performance of the converter in protecting the PEM EL during transient operations while guaranteeing correct specific energy consumption.
Cow Dung Gasification Process for Hydrogen Production Using Water Vapor as Gasification Agent
Jun 2022
Publication
In recent years with the development of hydrogen energy economy there is an increasing demand for hydrogen in the market and hydrogen production through biomass will provide an important way to supply clean environmentally friendly and highly efficient hydrogen. In this study cow dung was selected as the biomass source and the efficiency of the biomass to hydrogen reaction was explored by coupling high temperature pyrolysis and water vapor gasification. The experimental conditions of gasification temperature water mass fraction heating rate and feed temperature were systematically studied and optimized to determine the optimal conditions for in situ hydrogen production by gasification of cow dung. The relationship of each factor to the yield of hydrogen production by gasification of cow dung semi-coke was investigated in order to elucidate the mechanism of the hydrogen production. The experiment determined the optimal operating parameters of in situ gasification: gasification temperature 1173 K water mass fraction 80% heating rate 10 K/min and feed temperature 673 K. The semi-coke treatment separated high temperature pyrolysis and water vapor gasification and reduced the influence on gasification of volatile substances such as tar extracted from pyrolysis. The increase of semi-coke preparation temperature increases the content of coke reduces the volatile matter and improves the yield of hydrogen; the small size of semi-coke particles and large specific surface area are beneficial to the gasification reaction.
Electrofuels from Excess Renewable Electricity at High Variable Renewable Shares: Cost, Greenhouse Gas Abatement, Carbon Use and Competition
Nov 2020
Publication
Increasing shares of variable renewable electricity (VRE) generation are necessary for achieving high renewable shares in all energy sectors. This results in increased excess renewable electricity (ERE) at times when supply exceeds demand. ERE can be utilized as a low-emission energy source for sector coupling through hydrogen production via electrolysis which can be used directly or combined with a carbon source to produce electrofuels. Such fuels are crucial for the transport sector where renewable alternatives are scarce. However while ERE increases with raising VRE shares carbon emissions decrease and may become a limited resource with several usage options including carbon storage (CCS). Here we perform a model based analysis for the German case until 2050 with a general analysis for regions with a high VRE reliance. Results indicate that ERE-based electrofuels could achieve a greenhouse gas (GHG) abatement of 74 MtCO2eq yearly (46% of current German transport emissions) by displacing fossil fuels at high fuel-cell electric vehicle (FCEV) shares at a cost of 250–320 V per tCO2eq. The capital expenditure of electrolysers was found not to be crucial for the cost despite low capacity factors due to variable ERE patterns. Carbon will likely become a limiting factor when aiming for stringent climate targets and renewable electricity-based hydrocarbon electrofuels replacing fossil fuels achieve up to 70% more GHG abatement than CCS. Given (1) an unsaturated demand for renewable hydrocarbon fuels (2) a saturated renewable hydrogen demand and (3) unused ERE capacities which would otherwise be curtailed we find that carbon is better used for renewable fuel production than being stored in terms of overall GHG abatement.
Green Hydrogen Production by Anion Exchange Membrane Water Electrolysis: Status and Future Perspectives
Jan 2023
Publication
Green hydrogen production i.e. produced on a CO2 -neutral basis through the electrolysis of water employing renewable electricity has attracted increasing attention. The electricity required is generated from Renewable Energy Sources (RES) for example wind energy hydropower or solar energy. Since neither the process of production nor the end products of H2 and O2 are harmful to the environment green hydrogen is climate neutral. Developing electrolysis technology is therefore a research topic to follow. Anion Exchange Membrane (AEM) Water Electrolysis (WE) is an innovative technology that couples the advantages of the more mature technologies of Proton Exchange Membrane (PEM) and conventional alkaline electrolysis with the potential to eliminate the drawbacks of both. AEMWE technology is in an evolutionary stage and involves more investigation on several research topics such as membrane and catalyst development and stability as well as alternative feeding solutions that do not compromise the availability of fresh water. These topics are addressed in this paper mentioning the state-of-the-art materials new promising ones and providing future research directions to improve AEMWE towards a most mature technology.
Graphene Oxide @ Nickel Phosphate Nanocomposites for Photocatalytic Hydrogen Production
Mar 2021
Publication
The graphene oxide @nickel phosphate (GO:NPO) nanocomposites (NCs) are prepared by using a one-pot in-situ solar energy assisted method by varying GO:NPO ratio i.e. 0.00 0.25 0.50 0.75 1.00 1.25 1.50 and 2.00 without adding any surfactant or a structure-directing reagent. As produced GO:NPO nanosheets exhibited an improved photocatalytic activity due to the spatial seperation of charge carriers through interface where photoinduced electrons transferred from NiPO4 to the GO sheets without charge-recombination. Out of the series the system 1.00 GO:NPO NC show the optimum hydrogen production activity (15.37 μmol H2 h−1) towards water splitting under the visible light irradiation. The electronic environment of the nanocomposite GO-NiO6/NiO4-PO4 elucidated in the light of advance experimental analyses and theoretical DFT spin density calculations. Structural advanmcement of composites are well correlated with their hydrogen production activity.
The Route from Green H2 Production through Bioethanol Reforming to CO2 Catalytic Conversion: A Review
Mar 2022
Publication
Currently a progressively different approach to the generation of power and the production of fuels for the automotive sector as well as for domestic applications is being taken. As a result research on the feasibility of applying renewable energy sources to the present energy scenario has been progressively growing aiming to reduce greenhouse gas emissions. Following more than one approach the integration of renewables mainly involves the utilization of biomass-derived raw material and the combination of power generated via clean sources with conventional power generation systems. The aim of this review article is to provide a satisfactory overview of the most recent progress in the catalysis of hydrogen production through sustainable reforming and CO2 utilization. In particular attention is focused on the route that starting from bioethanol reforming for H2 production leads to the use of the produced CO2 for different purposes and by means of different catalytic processes passing through the water–gas shift stage. The newest approaches reported in the literature are reviewed showing that it is possible to successfully produce “green” and sustainable hydrogen which can represent a power storage technology and its utilization is a strategy for the integration of renewables into the power generation scenario. Moreover this hydrogen may be used for CO2 catalytic conversion to hydrocarbons thus giving CO2 added value.
A Review of the Use of Electrolytic Cells for Energy and Environmental Applications
Feb 2023
Publication
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.
Green Energy by Hydrogen Production from Water Splitting, Water Oxidation Catalysis and Acceptorless Dehydrogenative Coupling
Feb 2023
Publication
In this review we want to explain how the burning of fossil fuels is pushing us towards green energy. Actually for a long time we have believed that everything is profitable that resources are unlimited and there are no consequences. However the reality is often disappointing. The use of non-renewable resources the excessive waste production and the abandonment of the task of recycling has created a fragile thread that once broken may never restore itself. Metaphors aside we are talking about our planet the Earth and its unique ability to host life including ourselves. Our world has its balance; when the wind erodes a mountain a beach appears or when a fire devastates an area eventually new life emerges from the ashes. However humans have been distorting this balance for decades. Our evolving way of living has increased the number of resources that each person consumes whether food shelter or energy; we have overworked everything to exhaustion. Scientists worldwide have already said actively and passively that we are facing one of the biggest problems ever: climate change. This is unsustainable and we must try to revert it or if we are too late slow it down as much as possible. To make this happen there are many possible methods. In this review we investigate catalysts for using water as an energy source or instead of water alcohols. On the other hand the recycling of gases such as CO2 and N2O is also addressed but we also observe non-catalytic means of generating energy through solar cell production.
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