Intermittent Renewable Energy Storage Research Articles

Chemical Bath Deposition of NiFe Alloy Anode for Efficient Alkaline Water Electrolyzer Integration.

Green hydrogen production from water splitting is a feasible way for intermittent renewable energy storage and utilization, where the exploration and scale-up preparation of high-performance anodic oxygen evolution electrocatalysts are critical prerequisites for its industrial-level applications. Herein, a chemical bath deposition of FeNi3 intermetallic alloys onto Ni mesh support is performed, which delivers a current density of 0.62 Acm-2 at 1.72 V versus reversible hydrogen electrode for alkaline water oxidation in 1 m KOH and an excellent electrolysis stability at 0.2 A cm-2 for over 300 h. Moreover, via 3D computational fluid dynamics simulation and flow field optimization, a homogeneous deposition of ≈5400 cm2 NiFe anode is demonstrated within 4 min using the developed flow bath reactor. Once integrating the as-prepared NiFe anodes into alkaline electrolyzer stack, the voltage variation between each unit cell is below 40 mV at a total operation current of 71 A, or ca. current density of 0.2 A cm-2, confirming the uniformity of this batch synthesis protocol and its great potential for industrial alkaline water electrolysis.

Biomass-Derived Hard Carbon for Sodium-Ion Batteries: Basic Research and Industrial Application.

Sodium-ion batteries (SIBs) have significant potential for applications in portable electric vehicles and intermittent renewable energy storage due to their relatively low cost. Currently, hard carbon (HC) materials are considered commercially viable anode materials for SIBs due to their advantages, including larger capacity, low cost, low operating voltage, and inimitable microstructure. Among these materials, renewable biomass-derived hard carbon anodes are commonly used in SIBs. However, the reports about biomass hard carbon from basic research to industrial applications are very rare. In this paper, we focus on the research progress of biomass-derived hard carbon materials from the following perspectives: (1) sodium storage mechanisms in hard carbon; (2) optimization strategies for hard carbon materials encompassing design, synthesis, heteroatom doping, material compounding, electrolyte modulation, and presodiation; (3) classification of different biomass-derived hard carbon materials based on precursor source, a comparison of their properties, and a discussion on the effects of different biomass sources on hard carbon material properties; (4) challenges and strategies for practical of biomass-derived hard carbon anode in SIBs; and (5) an overview of the current industrialization of biomass-derived hard carbon anodes. Finally, we present the challenges, strategies, and prospects for the future development of biomass-derived hard carbon materials.

Nano-graphitic crystallites effect on the improved K-ion intercalation properties of Kigelia Africana fruit-derived hard carbon for potassium-ion batteries

The development of intermittent renewable energy storage technology is essential for building a sustainable, low-carbon society. Potassium-ion (K-ion) batteries are being extensively explored as alternate energy storage devices due to their closest redox potential and similarities to Lithium (Li) and Sodium (Na) batteries. Identifying alternate carbonaceous materials is, therefore, crucial to overcome the shortcomings of graphite. In this context, hard carbon derived from cellulose-rich Kigelia Africana fruit (KAP) was pyrolyzed at 1000 °C and 1100 °C and characterized using various techniques. The employed facile direct carbonization retains the inherent oxygen atoms (6.6 %). It restricts the growth of graphitic crystallites in the ab plane, thereby reducing the d-spacing revealed by X-ray Diffraction (XRD) and Raman Spectral analysis. The enhanced K-ion storage through insertion, as corroborated by Cyclic Voltammetry (CV) through the increased kinetics at the low potential < 0.5 V vs K/K+. The Galvanostatic Charge-Discharge (GCD) analysis further substantiates the role of graphitic nanocrystallites combined with the adsorption of O-atoms through the improved rate capability of KAP-1100 (110 mAh/g at 200 mA/g). On the other hand, KAP-1000 provides 10 mAh/g at 200 mA/g, which is almost ten times lower. Galvanostatic Intermittent Titration Technique (GITT) and Electrochemical Impedance Spectroscopy (EIS) analysis further prove the efficient diffusion coefficient (1.5 × 10-8 cm2/s) of K-ions in the hard carbon and low charge transfer resistance (Rct). This study reveals the effect of local structure and the inherently available heteroatom for developing better anodes for K-ion batteries.

Operando Identification of Temperature-Dependent Pore-Scale Gas Saturations in PEM Water Electrolyzers

Polymer electrolyte membrane (PEM) water electrolysis is a promising solution for the chemical storage of intermittent renewable energy in the form of clean hydrogen (1). For the widespread adoption of this technology, the efficiency of PEM electrolyzers must be improved through informed material design and tailored operating conditions to compete with incumbent carbon-emitting technologies (2). A main source of inefficiency is related to mass transport losses, where oxygen gas, a by-product of the anode reaction, accumulates in the anode porous transport layer (PTL) and hinders reactant liquid water delivery to reaction sites (3). Although extensive studies have explored this two-phase flow phenomenon, the consideration of operating temperature on gas accumulation in the PTL adds further complexity. A duality in temperature effects has been reported in the literature where increasing the operating temperature may encourage gas coverage which obstructs liquid water transport, but it may also enhance liquid water delivery due to favorable fluid property changes in viscosity and surface tension (4). Efforts have been made previously to reconcile these competing observations using 2D visualization methods (5), however a closer investigation using 3D visualization techniques will provide valuable pore-scale insights in the comprehensive understanding of the impact of operating temperature on gas transport in the PTL, and subsequently mass transport losses in the PEM electrolyzer.In this work, we employed operando X-ray computed tomography (CT) to visualize three-dimensional (3D) pore-scale gas saturations in the PTL at various industrially relevant operating conditions. Specifically, a custom in-house electrolyzer was imaged with synchrotron CT at five different temperatures (40°C, 50°C, 60°C, 70°C, 80°C) and current densities ranging from 0.5 A/cm² to 4.0 A/cm² with 0.5 A/cm² incremental steps. Electrochemical impedance spectroscopy and Tafel measurements were also acquired to characterize the relationship between gas distributions and corresponding mass transport overpotentials. Considering X-ray transparency, a model PTL made of carbon fibers was used to achieve sufficient contrast to quantify water and gas in the obtained images. Using precise volume registration and subtraction methods, pore-scale gas distributions in the PTL were quantified to reveal changes in bubble accumulation and coverage area at different operating temperatures and over operation time. The novel insights from this work will aid in our understanding of the complex relationship between operating temperature and multiphase flow phenomena in the PTL, which is vital for tailoring operating conditions of PEM electrolyzers to curtail the costs of green hydrogen production.

Cobalt(II)-complex modified Ag electrode for efficient and selective electrochemical reduction of CO2 to CO

Electrochemical conversion of CO2 into CO, powered by renewable electricity, offers one means to address the need for the storage of intermittent renewable energy. However, it is challenging because the competing HER is hard to avoid, which significantly compromises the selectivity to CO and reduces the efficiency of CO2RR devices. This study reports a cooperative catalyst design of metal–molecule catalyst interfaces with the goal of high local concentration of CO2 and stabilizing the intermediate, which improves the electrosynthesis of CO. The strategy is implemented by functionalizing the silver surface with cobalt (II)-complexes to promote the selective electrolysis of CO2 to CO. We report a CO2-to-CO Faradaic efficiency of 98.5 % and a partial current density of 16.52 mA cm−2 at − 1.1 V vs. RHE. Mechanism studies reveal that the catalytic performance of the Ag/Co(bpy)32+ correlates with the metal–molecule interaction, which provide new opportunities for construction and design of high-efficient catalysts toward CO2 reduction.

Optimal Incorporation of Intermittent Renewable Energy Storage Units and Green Hydrogen Production in the Electrical Sector

This paper presents a mathematical programming approach for the strategic planning of hydrogen production from renewable energies and its use in electric power generation in conventional technologies. The proposed approach aims to determine the optimal selection of the different types of technologies, electrolyzers and storage units (energy and hydrogen). The approach considers the implementation of an optimization methodology to select a representative data set that characterizes the total annual demand. The economic objective aims to determine the minimum cost, which is composed of the capital costs in the acquisition of units, operating costs of such units, costs of production and transmission of energy, as well as the cost associated with the emissions generated, which is related to an environmental tax. A specific case study is presented in the Mexican peninsula and the results show that it is possible to produce hydrogen at a minimum sale price of 4200 $/tonH2, with a total cost of $5.1687 × 106 and 2.5243 × 105 tonCO2eq. In addition, the financial break-even point corresponds to a sale price of 6600 $/tonH2. The proposed model determines the trade-offs between the cost and the emissions generated.

Transient characteristics of a solid oxide electrolysis cell under different voltage ramps: Transport phenomena behind overshoots

A promising solution to the storage of intermittent renewable energy is to integrate solid oxide electrolysis cells (SOEC) with solar/wind power. This trend necessitates comprehensive, quantitative investigations on the transient characteristics of SOEC, especially under varying power-supply conditions. For this purpose, a high-resolution, 3-dimensional, transient numerical model, as well as an adaptive time-stepping strategy, is proposed in this study. This study analyzes the electrical, gaseous, and thermal responses of SOEC to voltage ramps with different ramp rates and ramp magnitudes. The results show that electrical undershoots or overshoots occur after fast voltage changes. This phenomenon reflects the discrepancies between the steady and transient current–voltage characteristics and may lead to unsteady hydrogen production rates in practice. The electrical undershoots or overshoots are caused by the different transfer rates in SOEC – electronic/ionic transfer rate is faster than mass transfer rate, and mass transfer rate is faster than heat transfer rate. Furthermore, the electrical undershoots or overshoots can be divided into two parts. One part is related to mass-transfer lag, and the other part is related to heat-transfer lag. The former can be alleviated or eliminated by simply slowing down the voltage ramp, while the latter needs a more effective control strategy other than merely adjusting the voltage ramps. Apart from the electrical conditions, cell structure also has significant impacts on the electrical responses, e.g., the rib and the length of channel are related to the non-uniform electrical responses in the functional layer. Finally, via a quantitative technique developed from linear time-invariant systems, it is shown that the electrical responses of SOEC are governed by two time constants in the functional layer, namely the mass-transfer time constant (estimated as τm,H2O,FL=0.00723s) and the heat-transfer time constant (estimated as τt,FL=180s).

Magnetically Induced CO2 Methanation In Continuous Flow Over Supported Nickel Catalysts with Improved Energy Efficiency.

A new selective and efficient catalytic system for magnetically induced catalytic CO2 methanation was developed, composed of an abundant iron-based heating agent, namely a commercial iron wool, combined with supported Nickel nanoparticles (Ni NPs) as catalysts. The effect of metal oxide support was evaluated by preparing different 10 wt % Ni catalyst (TiO2 , ZrO2 , CeO2 , and CeZrO2 ) via organometallic decomposition route. As-prepared catalysts were thoroughly characterized using powder X-ray diffraction, electron microscopy, elemental analysis, vibrating sample magnetometer, and X-ray photoelectron spectroscopy techniques. High conversion and selectivity toward methane were observed at mid-temperature range, hence improving energy efficiency of the process with respect to the previous results under magnetic heating conditions. To gain further insight into the catalytic system, the effects of the synthesis method and of 0.5 wt % Ru doping were evaluated. Finally, the dynamic nature of magnetically induced heating was demonstrated through fast stop-and-go experiments, proving the suitability of this technology for the storage of intermittent renewable energy through P2G process.

Activated Single-Phase Ti4 O7 Nanosheets with Efficient Use of Precious Metal for Inspired Oxygen Reduction Reaction.

Invited for the cover of this issue is the group of Yu Wang, Feipeng Wang, and co-workers at Chongqing University. The image depicts how activated single-crystal Ti4 O7 nanosheets loaded with precious metals can be used as highly efficient and stable materials to make fuel-cell electrodes for intermittent renewable energy storage in power grids. Read the full text of the article at 10.1002/chem.202202580.

Pulsed electrolysis of carbon dioxide by large‐scale solid oxide electrolytic cells for intermittent renewable energy storage

AbstractCO2 electrolysis with solid oxide electrolytic cells (SOECs) using intermittently available renewable energy has potential applications for carbon neutrality and energy storage. In this study, a pulsed current strategy is used to replicate intermittent energy availability, and the stability and conversion rate of the cyclic operation by a large‐scale flat‐tube SOEC are studied. One hundred cycles under pulsed current ranging from −100 to −300 mA/cm2 with a total operating time of about 800 h were carried out. The results show that after 100 cycles, the cell voltage attenuates by 0.041%/cycle in the high current stage of −300 mA/cm2, indicating that the lifetime of the cell can reach up to about 500 cycles. The total CO2 conversion rate reached 52%, which is close to the theoretical value of 54.3% at −300 mA/cm2, and the calculated efficiency approached 98.2%, assuming heat recycling. This study illustrates the significant advantages of SOEC in efficient electrochemical energy conversion, carbon emission mitigation, and seasonal energy storage.

SNG based energy storage systems with subsurface CO2storage

Power-to-gas-to-power technologies incorporating electrolysis, methanation, SNG-fired Allam cycles and subsurface storages allow for a confined and circular use of CO2/CH4and thus an emission-free seasonal storage of intermittent renewable energy.

Parametric Study of a Long-Duration Energy Storage Using Pumped-Hydro and Carbon Dioxide Transcritical Cycles

The urgent energy transition needs a better penetration of renewable energy in the world’s energy mix. The intermittency of renewables requires the use of longer-term storage. The present system uses water displacement, in a lined rock cavern or in an aerial pressurised vessel, as the virtual piston of compressor and expander functions in a carbon dioxide heat pump cycle (HPC) and in an organic transcritical cycle (OTC). Within an impermeable membrane, carbon dioxide is compressed and expanded by filling and emptying pumped-hydro water. Carbon dioxide exchanges heat with two atmospheric thermal storage pits. The hot fluid and ice pits are charged by the HPC when renewable energy becomes available and discharged by the OTC when electricity is needed. A numerical model was built to replicate the system’s losses and to calculate its round-trip efficiency (RTE). A subsequent parametric study highlights key parameters for sizing and optimisation. With an expected RTE of around 70%, this CO2 PHES (pumped-hydro electricity storage) coupled with PTES (pumped thermal energy storage) could become a game-changer by allowing the efficient storage of intermittent renewable energy and by integrating with district heating and cooling networks, as required by cities and industry in the future.

Evaluation of a trigeneration system based on adiabatic compressed air energy storage and absorption heat pump: Thermodynamic analysis

Compressed air energy storage can be a promising application to meet diversified energy needs of cooling, heating and power supplies through mutual conversions among electrical, thermal and potential energies. A novel trigeneration system based on adiabatic compressed air energy storage is thus proposed for efficient allocation and utilization of the heat of compression. An absorption heat pump is also integrated in the system to improve the heat capacity of the proposed system. A steady state thermodynamic model of this system is then established with the focus on the energy conversion variation principle for changing key physical parameters. It is demonstrated that increasing storage pressure from 3 to 8 MPa can enhance the system round trip efficiency and exergy efficiency about 20.57–31.69% and 23.64–30.62%, respectively. Larger charge-discharge pressure difference has a negative effect on the two indicators. Minimal exergy efficiency can be found with the ratio of thermal oil allocation located at about 0.8. Lower vapor generator temperature and evaporation temperature can achieve higher system round trip efficiency and exergy. However, the influence is minor when evaporation temperature is higher than 283.15. In brief, this study represents detailed guidance for the design of the proposed system, which has a promising prospect in intermittent renewable energy storage and management.

Benchmarking of oxygen evolution catalysts on porous nickel supports

Summary Active and inexpensive oxygen evolution reaction (OER) electrocatalysts are needed for energy-efficient electrolysis applications. Objective comparison between OER catalysts has been blurred by the use of different supports and methods to evaluate performance. Here, we selected nine highly active transition-metal-based catalysts and described their synthesis, using a porous nickel foam and a new Ni-based dendritic material as the supports. We designed a standardized protocol to characterize and compare the catalysts in terms of structure, activity, density of active sites, and stability. NiFeSe- and CoFeSe-derived oxides showed the highest activities on our dendritic support, with low overpotentials of η100 ≈ 247 mV at 100 mA cm–2 in 1 M KOH. Stability evaluation showed no surface leaching for 8 h of electrolysis. This work highlights the most active anode materials and provides an easy way to increase the geometric current density of a catalyst by tuning the porosity of its support.

Dynamic modelling of methanation reactors during start-up and regulation in intermittent power-to-gas applications

Power-to-gas is a pathway for the storage of intermittent renewable energy in a chemical form; energy surpluses can be exploited to produce hydrogen (via electrolysis) that can then react with carbon dioxide to produce synthetic methane by using catalytic cooled reactors. Methanation unit has been designed and optimized, defining the number of involved reactors, the number of parallel tubes for each reactor and the staged CO2 injection to moderate the maximum temperature throughout the reactors. The produced synthetic natural gas (SNG) must have a methane content at least equal to 95 mol.-%, achieved by involving a series of 3 cooled reactors. Dynamic behavior of the as-designed system has been investigated for two cases that can occur when a power-to-gas system is operated intermittently: start-up from reactor hot standby and system operated at partial load. Methanation system requires about 130 s to reach the targeted methane content when it is started up from hot standby. In order to broaden the system rangeability (the minimum percentage of full load), different CO2 staged injection should be carried out: part of carbon dioxide bypasses first and second reactor and it is directly conveyed to the third one.

Electrochemical CO2 Reduction to Ethanol with Copper-Based Catalysts

Electrochemical CO2 reduction presents a sustainable route to storage of intermittent renewable energy. Ethanol is an important target product, which is used as a fuel additive and as a chemical feedstock. However, electrochemical ethanol production is challenging, as it involves the transfer of multiple electrons and protons alongside C–C bond formation. To date, the most commonly employed and effective catalysts are copper-based materials. This Review presents and categorizes the most efficient and selective Cu-based electrocatalysts, which are divided into three main groups: oxide-derived copper, bimetallics, and copper- and nitrogen-doped carbon materials. Only a few other specific examples fall outside this classification. The catalytic performance of these materials for ethanol production in aqueous conditions is discussed in terms of current density, overpotential, and faradaic efficiency. A critical evaluation of the factors that contribute to high performance is provided to aid the design of more efficient catalysts for selective ethanol formation.

DFTB Modeling of Lithium-Intercalated Graphite with Machine-Learned Repulsive Potential

Lithium ion batteries have been a central part of consumer electronics for decades. More recently, they have also become critical components in the quickly arising technological fields of electric mobility and intermittent renewable energy storage. However, many fundamental principles and mechanisms are not yet understood to a sufficient extent to fully realize the potential of the incorporated materials. The vast majority of concurrent lithium ion batteries make use of graphite anodes. Their working principle is based on intercalation, the embedding and ordering of (lithium-) ions in two-dimensional spaces between the graphene sheets. This important process, it yields the upper bound to a battery's charging speed and plays a decisive role in its longevity, is characterized by multiple phase transitions, ordered and disordered domains, as well as nonequilibrium phenomena, and therefore quite complex. In this work, we provide a simulation framework for the purpose of better understanding lithium-intercalated graphite and its behavior during use in a battery. To address large system sizes and long time scales required to investigate said effects, we identify the highly efficient, but semiempirical density functional tight binding (DFTB) as a suitable approach and combine particle swarm optimization (PSO) with the machine learning (ML) procedure Gaussian process regression (GPR) as implemented in the recently developed GPrep package for DFTB repulsion fitting to obtain the necessary parameters. Using the resulting parametrization, we are able to reproduce experimental reference structures at a level of accuracy which is in no way inferior to much more costly ab initio methods. We finally present structural properties and diffusion barriers for some exemplary system states.

Density Functional Tight Binding Modelling of Lithium Intercalated Graphite with Machine-Learned Repulsive Potential

Lithium ion batteries have been a central part of consumer electronics for decades. More recently, they have also become critical components in the quickly arising technological fields of electric mobility and intermittent renewable energy storage. However, many fundamental principles and mechanisms are not yet understood to a sufficient extent to fully realize the potential of the incorporated materials.The vast majority of concurrent lithium ion batteries make use of graphite anodes. Their working principle is based on intercalation–the embedding and ordering of (lithium-) ions in the two-dimensional spaces between the graphene sheets. This important process–it yields the upper bound to a battery's charging speed and plays a decisive role for its longevity–is characterized by multiple phase transitions, ordered and disordered domains, as well as non-equilibrium phenomena, and therefore quite complex. Such complexity emerges particularly at low states of charge (SOC), and complicates both the interpretation of experiments and the computational modelling.From a computational standpoint, targeted system sizes compatible with the SOC range of interest are inaccessible to first-principles calculations, yet require first-principles treatment of key effects such as dispersion and long-range electrostatics. Density Functional Tight Binding (DFTB), a semi-empirical approximation to DFT, offers a high-quality trade-off between accuracy and speed. However, this advantage comes at the cost–or rather initial investment–of pairwise parametrization.As no Li-C DFTB parameters were publicly available yet, we produced a parameter set specifically tailored to this system, employing a parametrization strategy [1] that combines global optimization of electronic parameters via Particle Swarm Optimization (PSO) [2] with our recently developed approach that uses Gaussian Process Regression (GPR) [3] to machine-learn the repulsive potential.Using the resulting parametrization, we are able to reproduce experimental reference structures at a level of accuracy which is in no way inferior to much more costly ab initio methods. We present structural properties and diffusion barriers for some exemplary system states. Additionally, we are able for the first time to resolve the full Potential Energy Surface (PES) of Li motion in stage-I and stage-II LiC108 (SOC 5%). The PES contains information that enables us to implement, and in perspective discuss, both kinetic Monte Carlo (kMC) models of Li-ion mobility in the graphite host, and free-energy sampling which ultimately yields the computed voltage profile of the anode.[1] Panosetti et al., https://arxiv.org/abs/1904.13351 [2] Chou et al., J. Chem. Theory Comput. 2016, 12, 1, 53–64[3] Panosetti et al., J. Chem. Theory Comput. 2020, 16, 4, 2181–2191 Figure 1

Highly Efficient Electroreduction of CO2 to C2+ Alcohols on Heterogeneous Dual Active Sites

AbstractElectroreduction of CO2 to liquid fuels such as ethanol and n‐propanol, powered by renewable electricity, offers a promising strategy for controlling the global carbon balance and addressing the need for the storage of intermittent renewable energy. In this work, we discovered that the composite composed of nitrogen‐doped graphene quantum dots (NGQ) on CuO‐derived Cu nanorods (NGQ/Cu‐nr) was an outstanding electrocatalyst for the reduction of CO2 to ethanol and n‐propanol. The Faradaic efficiency (FE) of C2+ alcohols could reach 52.4 % with a total current density of 282.1 mA cm−2. This is the highest FE for C2+ alcohols with a commercial current density to date. Control experiments and DFT studies show that the NGQ/Cu‐nr could provide dual catalytic active sites and could stabilize the CH2CHO intermediate to enhance the FE of alcohols significantly through further carbon protonation. The NGQ and Cu‐nr had excellent synergistic effects for accelerating the reduction of CO2 to alcohols.

Highly Efficient Electroreduction of CO2 to C2+ Alcohols on Heterogeneous Dual Active Sites.

Electroreduction of CO2 to liquid fuels such as ethanol and n-propanol, powered by renewable electricity, offers a promising strategy for controlling the global carbon balance and addressing the need for the storage of intermittent renewable energy. In this work, we discovered that the composite composed of nitrogen-doped graphene quantum dots (NGQ) on CuO-derived Cu nanorods (NGQ/Cu-nr) was an outstanding electrocatalyst for the reduction of CO2 to ethanol and n-propanol. The Faradaic efficiency (FE) of C2+ alcohols could reach 52.4 % with a total current density of 282.1 mA cm-2 . This is the highest FE for C2+ alcohols with a commercial current density to date. Control experiments and DFT studies show that the NGQ/Cu-nr could provide dual catalytic active sites and could stabilize the CH2 CHO intermediate to enhance the FE of alcohols significantly through further carbon protonation. The NGQ and Cu-nr had excellent synergistic effects for accelerating the reduction of CO2 to alcohols.