Intermittent Renewable Electricity Research Articles

Rational Design of Local Reaction Environment for Electrocatalytic Conversion of CO2 into Multicarbon Products

AbstractThe electrocatalytic conversion of CO2 into multi‐carbon (C2+) products provides an attractive route for storing intermittent renewable electricity as fuels and feedstocks with high energy densities. Although substantial progress has been made in selective electrosynthesis of C2+ products via engineering the catalyst, rational design of the local reaction environment in the vicinity of catalyst surface also acts as an effective approach for further enhancing the performance. Here, we discuss recent advances and pertinent challenges in the modulation of local reaction environment, encompassing local pH, the choice of the species and concentrations of cations and anions as well as local reactant/intermediate concentrations, for achieving high C2+ selectivity. In addition, mechanistic understanding in the effects of the local reaction environment is also discussed. Particularly, the important progress extracted from in situ and operando spectroscopy techniques provides insights into how local reaction environment affects C−C coupling and key intermediates formation that lead to reaction pathways toward a desired C2+ product. The possible future direction in understanding and engineering the local reaction environment is also provided.

Renewable hydrogen production through electrolysis: An analysis of the cost gap for its economic competitiveness in Italy

With global policies targeting greenhouse gas emission reduction, renewable hydrogen produced by water electrolysis powered with renewable electricity appears a promising alternative to fossil fuels. However, still high capital costs, reliance on intermittent renewable electricity sources, and high electricity cost hinder the economic viability of electrolyzers. This work develops a comprehensive analysis for assessing the need of an incentive to make renewable hydrogen economically viable, identifying different archetypes of electrolysis plant representative of a wide range of applications. A techno-economic optimization model is set up that minimize the average hydrogen production cost and compute the cost gap that makes hydrogen economically competitive with the fossil alternative, defining the optimal size and operation of the plant components while satisfying the hydrogen demand. The model is applied to the Italian case study. Sensitivity analyses investigate the impact of economy of scales, renewable electricity availability and introduction of the emission trading system. Cost gaps ranging between 8.1 €/kg and 29.9 €/kg highlights the need of an incentive to allow the deployment of this technology, thus meeting the hydrogen penetration targets.

Impact of intermittent electricity supply on a conceptual process design for microbial conversion of CO2 into hexanoic acid

Combining intermittent renewable electricity (IRE) with carbon capture and utilisation is urgently needed in the chemical sector. In this context, microbial electrosynthesis (MES) has gained attention. It can electrochemically produce hexanoic acid, a value-added chemical, from CO2. However, there is a lack of understanding regarding how the intermittency of renewable electricity could impact the design of a MES plant. We studied this using Aspen Plus models.A MES plant that was powered by constant grid electricity could operate from 100% down to 70% of its nominal capacity, at which point the heat exchangers and the internal geometrical design of the distillation towers became bottlenecks. The levelised production cost of hexanoic acid (LPCC6A) was estimated at 4.0 €/kg. Switching to IRE supply increased LPCC6A to 5.3 €/kg (for wind electricity) and 4.7 €/kg (for hybrid renewable electricity).A battery energy storage system (BESS) was deployed. The lowest LPCC6A was found at a BESS installation of 29 GJ/h for wind electricity (5.1 €/kg) and at 12 GJ/h for hybrid renewable electricity (4.7 €/kg). In both situations, the volume flexibility of the MES plant was not improved. At the investigated market and operating conditions, coupling IRE to the MES plant was economically infeasible.

Nanometer-Resolved Operando Photo-Response of Faceted BiVO4 Semiconductor Nanoparticles.

Photo(electro)catalysis with semiconducting nanoparticles (NPs) is an attractive approach to convert abundant but intermittent renewable electricity into stable chemical fuels. However, our understanding of the microscopic processes governing the performance of the materials has been hampered by the lack of operando characterization techniques with sufficient lateral resolution. Here, we demonstrate that the local surface potentials of NPs of bismuth vanadate (BiVO4) and their response to illumination differ between adjacent facets and depend strongly on the pH of the ambient electrolyte. The isoelectric points of the dominant {010} basal plane and the adjacent {110} side facets differ by 1.5 pH units. Upon illumination, both facets accumulate positive charges and display a maximum surface photoresponse of +55 mV, much stronger than reported in the literature for the surface photo voltage of BiVO4 NPs in air. High resolution images reveal the presence of numerous surface defects ranging from vacancies of a few atoms, to single unit cell steps, to microfacets of variable orientation and degree of disorder. These defects typically carry a highly localized negative surface charge density and display an opposite photoresponse compared to the adjacent facets. Strategies to model and optimize the performance of photocatalyst NPs, therefore, require an understanding of the distribution of surface defects, including the interaction with ambient electrolyte.

Efficient Synthesis of Nitric Acid Under Air Atmosphere with Lattice-Confined Ru Clusters

Nitrate (NO3 -) is an important industrial chemical used as fertilizers in agriculture, as well as oxidizing agents in explosives. Today, NO3 - is manufactured predominantly via an Ostwald process by oxidizing ammonia (NH3), and the ammonia used here comes primarily from the Haber–Bosch (HB) process.However, this process operates at high temperatures (300–500 °C) and pressures (200–300 bar), and requires a coupled steam reforming plant for hydrogen (H2) production. As a result, approximately 1.9 metric tons of CO2 is formed per metric ton of NH3 produced, contributing significantly to climate change. In addition, due to the complexity of the Ostwald and Haber-Bosch processes, it is only economical at large scales, leading to centralized production, which situation is poorly matched with the distributed nature of HNO3 utilization. Therefore, it is highly desirable to bypass the ammonia route and develop a direct and sustainable approach for HNO3 synthesis.Electrochemical synthesis of chemicals has been regarded as an attractive alternative to traditional thermochemical methods. In electrochemical reactions, electric potential can replace high temperature and pressure as the thermodynamic driving force.Therefore, direct electrochemical oxidation of molecular nitrogen appears to be a very potential approach for HNO3 synthesis,which could be sustainable, modular and easily integrated with intermittent renewable electricity. However, due to the lack of natural or artificial electrocatalysts as a reference, the nitrogen oxidation reaction (NOR) remains largely unexplored despite its enormous practical value as a replacement for the fossil fuel-driven two-step HNO3 preparation approach.Until 2019, Zhang et al. reported the first experimental NOR electrocatalyst composed of well-dispersed Pd nanoparticles on MXene nanosheets that can effectively convert N2 into nitrate, which definitely proved the feasibility of using electrochemistry to motivate the endothermic NOR at ambient conditions. Unfortunately, to date, there are still only a few works that reported the electrosynthesis of nitrate from nitrogen, and the proposed electrocatalysts can only achieve limited NOR activity.An in-depth exploration of the NOR process, which consists of two main steps: the first step is a rate-limiting step that converts inert N2 into the active NO* intermediate; the second step is a nonelectrochemical step where NO* reacts with H2O and the generated O* from electrocatalytic water splitting to form nitrate. Therefore, the main factors restricting the development of the electrochemical nitrate synthesis technology can be inferred as follows: (1) the strong N≡N triple bond in the dinitrogen molecule (bond energy: 940.95 kJ mol−1) is highly challenging to oxidate nitrogen to nitrate under mild conditions; (2) the potential window between the NOR and oxidation evolution reaction (OER) is quite narrow, and thus the latter as a competitive reaction can severely restrict the selectively of the nitrogen oxidation synthesis of nitrate; (3) the extremely low solubility and diffusion coefficient of N2 in aqueous electrolytes can significantly inhibit the nitrogen available for the reaction, resulting in unfavorable NOR performance. Therefore, to overcome the above obstacles, extensive studies should focus on designing efficient nitrogen oxidation catalysts and improving electrochemical reaction systems to promote NOR and suppress OER.In the present work, we firstly discovered that synthesizing Ru particles grow along the TiO2 lattice (Ru-TiO2) as the working electrode and can achieve excellent NOR performance by using air as a gas source. Textural analysis sufficiently demonstrates that the matching lattice constants of metal Ru and TiO2 allow the Ru to be confined in the TiO2 lattice, leading to the formation of Ru-Ti bonds and the transfer of electrons from TiO2 to Ru metal. Our results reveal that the electron redistribution of Ru-TiO2 can significantly alter the electronic structure of Ru, leading to the formation of highly occupied Ru 4d bands, which can effectively change the adsorption of surface species and improve the NOR activity. In addition, the Ru confined in TiO2 exhibits particularly high stability towards NOR up to potentials above 1.7 V (versus RHE). As a result, Ru-TiO2 could achieve a record-high NOR performance with a nitric acid yield rate of 18.71 ug h-1 cm-2 (150.2 μmol h-1 g-1) and Faraday efficiency of 25.17% in the air atmosphere. This discovery suggests that the surface oxophilicity and electronic structure of metal particles can be effectively modified by lattice confinement in semiconductors and offers an alternative concept for designing catalysts with unique properties for use in catalysis and beyond. Figure 1

High-Performance CO2 and H2O Co-Electrolysis Based on Micro-Structured Hollow Fiber Solid Oxide Electrolysis Cell

The world is dedicated to achieving Carbon Neutrality and Circular Economy in the next decades by circulating carbon element. This makes the research related to energy and environment more stringent and urgent. Solid oxide electrolysis cell (SOEC) has been regarded as the key enabling technologies to mitigate the issues and meanwhile can take full use of the intermittent renewable electricity. Herein, we designed a multi-channel hollow fiber SOEC, which presents sub-millimeter channels and separate domains of mechanical strength and catalytic reactions, to split CO2 (and H2O) to CO (and H2), which can be used as the feedstock for Fischer-Tropsch and methanol synthesis. The results show high current density, good performance durability, and low concentration polarization, and thus the new design can achieve compact design together with excellent performance with volumetric productivity of above 125 kmol/m3/hr at 750 degC. Co-electrolysis performance is further explored by incorporating newly designed catalyst for further enhancement. Figure 1

Electrochemical CO2 Reduction to Formic Acid As Feedstock for Biotechnological Processes

Substituting fossil-based production methods with methods utilizing renewable resources is experiencing growing interest. Incorporating intermittent renewable electricity into such processes is highly desirable, especially for energy storage purposes. In this context, electrocatalytic conversion of renewable raw materials into platform chemicals is an important approach. Biogenic raw materials can be converted into platform chemicals through electrocatalysis, which can then be used in power-to-X-to-Y processes to generate a range of products. One notable example of this approach is the electrochemical conversion of CO2 into formic acid, which has numerous applications in the chemical, textile, agricultural, and pharmaceutical industries [1, 2]. Utilization of CO2-based formate as a microbial substrate is a fascinating research topic that expands the range of possible products. The work presented here focuses on optimizing a compatible interface between efficient electrochemical processs and biotechnology, by identifying key factors, including the choice of catalyst, electrolyte, electrochemical setup, and formate production rate. This study also involves testing of an electrochemical microreactor for the scalable production of formate from CO2. Our results show that formate concentrations of up to 3 mol L-1 can be achieved in a bio-compatible buffer electrolyte using an optimized electrochemical process at high current densities. Additionally, this research successfully demonstrates the biochemical utilization of electrochemically produced CO2-based formate in coupled electro-biochemical processes. The developed process is a sustainable and efficient method for producing value-added products from CO2 and renewable electric energy, contributing to bridging the gap between electrochemical and biological processes.

Electrocatalytic valorization of lignocellulose-derived aromatics at industrial-scale current densities

Electrocatalytic hydrogenation of lignocellulosic bio-oil to value-added chemicals offers an attractive avenue to use the increasing intermittent renewable electricity and biomass-derived feedstocks. However, to date the partial current densities to target products of these reactions are lower than those needed for industrial-scale productivity, which limits its prospects. Here we report a flow-cell system equipped with a Rh diffusion electrode to hydrogenate lignocellulose-derived aromatic monomers, such as furans and lignin monomers, to value-added chemicals. We achieve high faradaic efficiencies up to 64% at industrial-scale current densities of 300–500 mA cm−2, representing high productivities to target products. A screening of electrocatalysts indicates that only by highly-electrolyte-permeable Rh diffusion electrodes are we able to unite current density with faradaic efficiency. We apply in-situ infrared reflection–absorption spectroscopy to investigate the electrode-potential-dependent reaction pathways and intermediates, confirming a wide potential window for efficient electrocatalytic hydrogenation of lignocellulose-derived aromatics to target products.

Tailoring the Hydrophobic Interface of Core-Shell HKUST-1@Cu2O Nanocomposites for Efficiently Selective CO2 Electroreduction.

The electrochemical reduction of carbon dioxide (CO2) to ethylene creates a carbon-neutral approach to converting carbon dioxide into intermittent renewable electricity. Exploring efficient electrocatalysts with potentially high ethylene selectivity is extremely desirable, but still challenging. In this report, a laboratory-designed catalyst HKUST-1@Cu2O/PTFE-1 is prepared, in which the high specific surface area of the composites with improved CO2 adsorption and the abundance of active sites contribute to the increased electrocatalytic activity. Furthermore, the hydrophobic interface constructed by the hydrophobic material polytetrafluoroethylene (PTFE) effectively inhibits the occurrence of hydrogen evolution reactions, providing a significant improvement in the efficiency of CO2 electroreduction. The distinctive structures result in the remarkable hydrocarbon fuels generation with high Faraday efficiency (FE) of 67.41%, particularly for ethylene with FE of 46.08% (-1.0V vs RHE). The superior performance of the catalyst is verified by DFT calculation with lower Gibbs free energy of the intermediate interactions with improved proton migration and selectivity to emerge the polycarbon（C2+） product. In this work, a promising and effective strategy is presented to configure MOF-based materials with tailored hydrophobic interface, high adsorption selectivity and more exposed active sites for enhancing the efficiency of the electroreduction of CO2 to C2+ products with high added value.

Dynamically Adaptive Bubbling for Upgrading Oxygen Evolution Reaction Using Lamellar Fern-Like Alloy Aerogel Self-Standing Electrodes.

Adopting renewable electricity to produce "green" hydrogen has been a critical challenge because at a high current density the mass transfer capability of most catalytic electrodes deteriorates significantly. Herein, a unique lamellar fern-like alloy aerogel (LFA) electrode, showing a unique dynamically adaptive bubbling capability and can effectively avoid stress concentration caused by bubble aggregation is reported. The LFA electrode is intrinsically highly catalytic-active and shows a highly porous, resilient, hierarchically ordered, and well-percolated conductive network. It not only shows superior gas evacuation capability but also exhibits significantly improved stability at high current densities, showing the record lowest oxygen evolution reaction (OER) overpotential of 244mV at 1000mA cm-2 and stably over 6000 h. With the merits of mechanical robustness, excellent electron transport, and efficient bubble evacuation, LFA can be self-standing catalytic electrode andgas diffusion layers in anion-exchange-membrane water electrolysis (AEMWE), which can achieve 3000 mA cm-2 at a low voltage of 1.88V and can sustain stable electrolysis at 2000 mA cm-2 for over 1300 h. This strategy can be extended to various gas evolution reactions as a general design rule for multiphase catalysis applications.

Advanced electrode enabled by lignin-derived carbon for high-performance vanadium redox flow battery

Vanadium redox flow batteries (VRFBs) are promising energy storage systems with the potential to bridge the gap between intermittent renewable electricity generation and continuous supply of reliable electricity. The electrodes found in VRFB cells affect their energy efficiency (EE) and power density. It is important to fabricate electrodes with intriguing properties to enable VRFBs to have high performance. Herein, the abundant and cost-effective lignin is employed as the precursor to produce amorphous carbon particles after undergoing thermal decomposition treatment. The carbon particles cover the surface of carbon felt (CF). The resulting CF modified by lignin-derived carbon particles (Lignin-CF) with increased active sites and improved hydrophilicity displays superior electrochemical activity towards the VO2+/VO2+ pair than both the pristine CF and the heated bare CF. Remarkably, the VRFB consisting of Lignin-CF which acts as the positive electrode shows high performance in terms of the average EE (83.3 %) and average voltage efficiency (VE) (85.0 %) over 1000 cycles (long cycling life) for more than 16 days at 100 mA cm−2, and high power density of 1053.2 mW cm−2. It is noted that the EE and VE are comparable to the highest reported value of CF modified by carbon-based materials, aside having evidently longer cycling life. This study provides a feasible strategy for fabricating an affordable electrode for high-performance VRFBs.

Accumulation of Liquid Byproducts in an Electrolyte as a Critical Factor That Compromises Long-Term Functionality of CO2-to-C2H4 Electrolysis.

Electrochemical conversion of CO2 using Cu-based gas diffusion electrodes opens the way to green chemical production as an alternative to thermocatalytic processes and a storage solution for intermittent renewable electricity. However, diverse challenges, including short lifetimes, currently inhibit their industrial usage. Among well-studied determinants such as catalyst characteristics and electrode architecture, possible effects of byproduct accumulation in the electrolyte as an operational factor have not been elucidated. This work quantifies the influence of ethanol, n-propanol, and formate accumulation on selectivity, stability, and cell potential in a CO2-to-C2H4 electrolyzer. Alcohols accelerated flooding by degrading the hydrophobic electrode characteristics, undermining selective and stable ethylene formation. Furthermore, high alcohol concentrations triggered the catalyst layer's abrasion and structural disfigurements in the Nafion 117 membrane, leading to high cell potentials. Therefore, continuous removal of alcohols from the electrolyte medium or substantial modifications in the cell components must be considered to ensure long-term performing CO2-to-C2H4 electrolyzers.

Analysis of Degradation Phenomena of SOC Stacks Operated in Reversible SOFC / SOEC Cycling Mode

The reversible SOFC/SOEC operation of solid oxide cell (SOC) stacks promise high overall electricity-to-electricity round-trip efficiencies and low storage costs. Although in recent years the degradation rates of SOFC and SOEC stacks in single mode long-term operation have been steadily decreased, the understanding of degradation mechanisms during reversible SOFC/SOEC operation remains an important and challenging issue. Therefore, the Korean-German project “Solid Oxide Reversible Fuel Cell / Electrolysis Stack” (SORFES) focuses on the development of the core component technology for a 1 kW reversible SOC stack in order to enhance the hydrogen productivity and its utilization. The primary goals are the improvement of the performance and the durability of SOC stacks during reversible SOFC/SOEC operation and the quantification and the qualification of the relevant degradation effects.The paper presents and compares the performance and degradation results of two SOC stacks which were operated mainly in galvanostatic steady-state SOFC mode and in reversible SOFC/SOEC cycling mode. The stacks with ASC cells of Elcogen (Estonia) were fabricated by the industrial project partner E&KOA (Daejeon, Korea). The reversible cycles consist of day/night switches between SOEC and SOFC, thus covering intermittent renewable electricity supply (e.g. of photovoltaics). The stacks were electrochemically characterized by jV-curves and electrochemical impedance spectroscopy (EIS).The first SOC stack with 10 cells was operated during 500 h in SOFC at constant current density followed by 500 h of operation under reversible SOFC/SOEC cycling conditions. The initial performance and homogeneity along the repeat units (RUs) of the stack in SOFC and SOEC at the beginning of operation are presented. In order to better understand the stack degradation, the results between reversible SOFC/SOEC cycling and galvanostatic steady-state SOFC operation are compared. The degradation, especially of the OCV, the power density and the area specific resistance (ASR) of the different RUs are analyzed and discussed. Moreover, the progression of the individual resistances, specifically of the ohmic-, the electrode polarization- and the gas concentration resistances of the RUs are evaluated and presented. The influence of temperature gradients and thermo-mechanical stresses during reversible exothermic (SOFC) and endothermic (SOEC) cycling are outlined and discussed.The results of the first stack test were used to improve the stack components and setup, e.g. the contacting and sealing of the cells in the stack and the protective coating on the interconnects. Moreover, the operating conditions during reversible SOFC/SOEC cycling were optimized. The second improved stack with 6 RUs was operated for 2800 h in galvanostatic steady-state SOFC mode and reversible SOFC/SOEC cycling mode with low degradation rate.The results of the present paper help to understand and improve the long-term stability of SOC stacks during reversible SOFC/SOEC cycling, thus promoting the SOC technology for renewable energy storage applications.

Design and analysis for chemical process electrification based on renewable electricity: Coal-to-methanol process as a case study

Electrification of traditional large-scale chemical industry based on renewable electricity can greatly reduce process CO2 emission, and store intermittent renewable electricity into chemical products locally to decrease power grid frequency regulation caused by fluctuating renewable electricity. This study presents a framework for electrification of chemical industry from indirect and direct aspects using the state-of-art coal-to-methanol process as a case study. Traditional coal-to-methanol (Process 1) suffers from high CO2 emission due to mismatch of H/C ratio between coal and methanol. A pulverized coal gasification-integrated SOEC process (Process 2) has been investigated, the water–gas-shift unit is avoided and a simplified acid gas removal process is implemented to replace traditional acid gas removal unit in Process 2. Electric heaters and heat pump system are applied in Process 2 as direct electrification methods to form semi-electrified scenario (Process 3). To discuss the effect of electrification levels on process performances, a fully electrified process (Process 4) is also designed. The results show that: CO2 emissions of the four processes are 2.19, 0.71, 0.52 and 0.63 t/t MeOH, and energy efficiency are 57.40 %, 62.32 %, 64.31 % and 57.63 %, respectively. Production costs are 159.1, 294.3, 301.0 and 358.3 $/t MeOH, IRRs are 14, 31, 29 and 14.5 %, respectively. Through this research and analysis, we hope to explore integration potential of renewable electricity and traditional chemical industry, and design a greener methanol production route based on renewable electricity.

AlCl3-NaCl-ZnCl2 Secondary Electrolyte in Next-Generation ZEBRA (Na-ZnCl2) Battery

Increasing demand to store intermittent renewable electricity from, e.g., photovoltaic and wind energy, has led to much research and development in large-scale stationary energy storage, for example, ZEBRA batteries (Na-NiCl2 solid electrolyte batteries). Replacing Ni with abundant and low-cost Zn makes the ZEBRA battery more cost-effective. However, few studies were performed on this next-generation ZEBRA (Na-ZnCl2) battery system, particularly on its AlCl3-NaCl-ZnCl2 secondary electrolyte. Its properties such as phase diagrams and vapor pressures are vital for the cell design and optimization. In our previous work, a simulation-assisted method for molten salt electrolyte selection has shown its successful application in development of molten salt batteries. The same method is used here to in-depth study the AlCl3-NaCl-ZnCl2 salt electrolyte in terms of its phase diagrams and vapor pressures via FactSageTM and thermo-analytical techniques (Differential Scanning Calorimetry (DSC) and OptiMeltTM), and their effects on battery performance such as operation safety and charging/discharging reaction mechanism. The DSC and OptiMelt results show that the experimental data such as melting temperatures and phase changes agree well with the simulated phase diagrams. Moreover, the FactSageTM simulation shows that the salt vapor pressure increases significantly with increasing temperature and molar fraction of AlCl3. The obtained phase diagrams and vapor pressures will be used in the secondary electrolyte selection, cell design and battery operation.

Comparative analysis of electrolyzers for electrochemical carbon dioxide conversion

Electrochemical carbon dioxide (CO2) conversion to fuels and chemicals provides a long-term and large-scale storage solution for intermittent renewable electricity. In the last few decades, most of the effort has been devoted to developing new catalysts to improve CO2 reduction performance. Very recently, advances in system design, including electrochemical cell design and electrochemical operating conditions, have led to a significant improvement in CO2 conversion efficiency. In this review, we describe system design strategies in the context of boosting key performance metrics in CO2 conversion: current density, Faradaic efficiency, energy efficiency, stability, reactant utilization and product concentration, carbonate formation and CO2 crossover. The advantages and limitations of each strategy, in terms of overall CO2 conversion performance, are discussed. This review offers guidelines for developing a high-performance electrochemical CO2 conversion system to bring this technology closer to practical implementation.

Contribution to net zero emissions of integrating hydrogen production in wastewater treatment plants

The reliability of renewable hydrogen supply for off-take applications is critical to the future sustainable energy economy. Integrated water electrolysis can be deployed at distributed municipal wastewater treatment plants (WWTP), creating opportunity for reduction in carbon emissions through direct and indirect use of the electrolysis output. A novel energy shifting process where the co-produced oxygen is compressed and stored to enhance the utilisation of intermittent renewable electricity is analysed. The hydrogen produced can be used in local fuel cell electric buses to replace incumbent diesel buses for public transport. However, quantifying the extent of carbon emission reduction of this conceptual integrated system is key. In this study, the integration of hydrogen production at a case study WWTP of 26,000 EP capacity and using the hydrogen in buses was compared with two conventional systems: the base case of a WWTP with grid electricity consumption offset by solar PV and the community's independent use of diesel buses for transport, and the non-integrated configuration with hydrogen produced at the bus refuelling location operated independently of the WWTP. The system response was analysed using a Microsoft Excel simulation model with hourly time steps over a 12-month time frame. The model included a control scheme for the reliable supply of hydrogen for public transport and oxygen to the WWTP, and considered expected reductions in carbon intensity of the national grid, level of solar PV curtailment, electrolyser efficiency and size of the solar PV system. Results showed that by 2031, when Australia's national electricity is forecast to achieve a carbon intensity of less than 0.186 kg CO2-e/kWh, integrating water electrolysis at a municipal WWTP for producing hydrogen for use in local hydrogen buses produced less carbon emissions than continuing to use diesel buses and offsetting emissions by exporting renewable electricity to the grid. By 2034, an annual reduction of 390 t–CO2–e is expected after changing to the integrated configuration. Considering electrolyser efficiency improvements and curtailment of renewable electricity, the reduction increases to 872.8 t–CO2–e.

Manipulating local coordination of copper single atom catalyst enables efficient CO2-to-CH4 conversion

Electrochemical CO2 conversion to methane, powered by intermittent renewable electricity, provides an entrancing opportunity to both store renewable electric energy and utilize emitted CO2. Copper-based single atom catalysts are promising candidates to restrain C-C coupling, suggesting feasibility in further protonation of CO* to CHO* for methane production. In theoretical studies herein, we find that introducing boron atoms into the first coordination layer of Cu-N4 motif facilitates the binding of CO* and CHO* intermediates, which favors the generation of methane. Accordingly, we employ a co-doping strategy to fabricate B-doped Cu-Nx atomic configuration (Cu-NxBy), where Cu-N2B2 is resolved to be the dominant site. Compared with Cu-N4 motifs, as-synthesized B-doped Cu-Nx structure exhibits a superior performance towards methane production, showing a peak methane Faradaic efficiency of 73% at −1.46 V vs. RHE and a maximum methane partial current density of −462 mA cm−2 at −1.94 V vs. RHE. Extensional calculations utilizing two-dimensional reaction phase diagram analysis together with barrier calculation help to gain more insights into the reaction mechanism of Cu-N2B2 coordination structure.

Value creation by converting pulp mill flue gas streams to green fuels

Climate change mitigation induces strong growth in renewable electricity production, partly driven by shifts in environmental policies and regulation. Intermittent renewable electricity requires supporting systems in the form of sustainable hydrocarbon chemicals such as transportation fuels. Bulk chemical production fits well into a pulp mill environment, given their large volumes, stable operation, and ample supply of biomass-based carbon feedstock in the form of flue gases. Until now, the utilization of the flue gases from conventional operation of a pulp mill has received little attention. Harnessing these flue gases into usable products could offer additional value to mill operators, while also diversifying their product portfolio. However, electricity-based fuels and products require extra energy in the conversion step and may not be commercially competitive with current fossil products under the current regulation. There might also be uncertainties about future commodity prices. Thus, the objective of this study is to estimate the economic competitiveness and the added value of selected side products that could be produced alongside conventional pulp and paper products. A typical modern pulp mill is modeled in different product configurations and operational environments, which allows testing of various development paths. This illustrates how the overall energy and mass balance of a pulp mill would react to changes in different final products and other parameters. The focus of the study is in synthetic methanol, which is produced from flue gases and excess resources from the mill, with minimal interference to the pulping process. The results aid in assessing the necessity and magnitude of a premium payment for subsidizing green alternatives to replace current fossil fuels and chemicals. Additionally, the results function as an indicator of the development state of the pulp and paper industry in the turmoil of climate change regulation. The results indicate that pow-er-to-X systems offer one more viable pathway alternative for broadening the product portfolio of the pulp and paper sector, as well as opening new flexibility measures and services to grid stabilization. Market conditions were found to have a significant impact on the perceived profitability.

Enabling independent flexibility service providers to participate in electricity markets: A legal analysis of the Belgium case

Ambitious renewables targets of the EU call for creating a flexible electricity system accommodating and facilitating the integration of large-scale intermittent renewable electricity. To further exploit the considerable potential of demand flexibility, final customers need to be fully mobilised to offer their flexibility to electricity markets. The independent flexibility service provider (IFSP) operates independently from the electricity supplier and has a separate balance responsible party (BRP), which plays a key role to that end. However, in activating demand flexibility, suppliers and BRPs are affected and thus likely to impose barriers or restrictions on market entry of IFSPs. This analysis utilizes legal-empirical research to closely examine how to promote broader market participation of IFSPs by regulating their relationships with affected suppliers and BRPs. In doing so, the Belgian regulatory framework is used as a case study. This article further analyses the remaining regulatory gaps and challenges of the Belgian framework.