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Svenja Bielefeld, Miloš Cvetković, Andrea Ramírez

Electrification of processes and utilities is considered a promising option towards the reduction of greenhouse gas emissions from the chemical industry. Therefore, electricity demand is expected to increase steeply. Since the sources of future low-carbon electricity are variable in nature, there is a need for strategies to match availability and demand. Literature identified the flexibility of chemical processes as one promising strategy to address variability. This study aims to provide insights into how stakeholders from the power sector and the chemical industry consider flexibility in chemical processes and to identify key benefits and bottlenecks. For this article, we combined a review of peer-reviewed and grey literature with stakeholder interviews to map and describe the state of the art of flexible chemicals production, and to identify requirements for further research. The main drivers to investigate the flexibility potential are first, the contribution to energy system reliability, and second, potential cost savings for the industry. Main limitations are considered to be first, the uncertain economic performance of flexible processes due to investment costs, reduced production and uncertain revenues from flexible operation, and second, the complexity of the implementation of flexibility.

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Hanna Trzesniowski, Nipon Deka, Onno van der Heijden, Ronny Golnak, Jie Xiao, Marc T. M. Koper, Robert Seidel, and Rik V. Mom

For electrocatalysts with a layered structure, ion intercalation is a common phenomenon. Gaining reliable information about the intercalation of ions from the electrolyte is indispensable for a better understanding of the catalytic performance of these electrocatalysts. Here, we take a holistic approach for following intercalation processes by studying the dynamics of the catalyst, water molecules, and ions during intercalation using operando soft X-ray absorption spectroscopy (XAS). Sodium and oxygen K-edge and nickel L-edge spectra were used to investigate the Na⁺ intercalation in a Ni_0.8Fe_0.2O_x electrocatalyst during the oxygen evolution reaction (OER) in NaOH (0.1 M). The Na K-edge spectra show an irreversible intensity increase upon initial potential cycling and a reversible intensity increase at the intercalation potential, 1.45 V_RHE, coinciding with an increase in the Ni oxidation state. Simultaneously, the O K-edge spectra show that the Na⁺ intercalation does not significantly impact the hydration of the catalyst.

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Francesco Mattarozzi, Karen van den Akker, Matt L. J. Peerlings, Maaike E. T. Vink-van Ittersum, Nienke L. Visser, Rim C. J. van de Poll, Prof. Dr. Emiel J. M. Hensen, Dr. Peter Ngene, Prof. Dr. Petra E. de Jongh

Silver electrocatalysts enable the conversion of CO₂ to CO, thereby facilitating the transition to a carbon neutral society. To lower the cost of the expensive metal, silver nanostructures are often supported on carbon. This substrate offers great electrical conductivity, but it enhances the selectivity towards the competing hydrogen evolution reaction. In this work, carbon supports were functionalized with linear alkylamines of different chain lengths, to understand its effect on electrochemical performance. Alkylamines interact with the carbon surface and confer hydrophobic properties to the carbon support as well as making the local environment less acidic. These properties led not only to a suppression of the hydrogen evolution, but also to a remarkable enhancement in CO production. Despite the low silver weight loading (0.0016 mg_Ag cm⁻²), hexylamine-functionalized carbon-based catalysts achieved a CO to H₂ ratio of 2.0, while the same material without the alkylamine functionalization only reached a ratio of 0.3, at −1.3 V vs RHE. This demonstrates the potential of hydrophobic functionalization for enhancing the CO selectivity of carbon-supported catalysts.

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N. van Uffelen, B. Taebi, Udo Pesch

Energy justice is often approached through the four tenets of procedural, distributive, restorative and recognition justice. Though these tenets are important placeholders for addressing what type of justice issues are involved, they require further normative substantiations. These are achieved by using principles of justice to specify why – normatively speaking – something is just or unjust within each category or tenet of justice. In addressing the principles of justice, it is important to acknowledge normative uncertainties, or the fact that different (incompatible) conceptions of justice might be morally defensible, leading to different normative conclusions or policy recommendations. This paper reviews the definitions of tenets in energy justice scholarship, the occurrence of normative claims, and how these claims are justified. The review shows that the scholarship ignores to a large extent normative uncertainties. In response, we propose a revisited energy justice framework, focusing on four aspects that help us to articulate the normative uncertainties in both the principles and the tenets of energy justice. These aspects are (i) the scale of justice (i.e. whether justice is considered at a local, national, regional, multinational or global scale), (ii) the subject of justice, (iii) the body of knowledge that is assumed and (iv) the time frame in which justice issues are being considered. We hope to provide a conceptual framework that make explicit the different types of normative assumptions underlying claims of justice, which will ultimately improve the quality and legitimacy of normative conclusions such as policy recommendations that follow.

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Sunghak Park, Luhao Liu, Çayan Demirkır, Onno van der Heijden, Detlef Lohse, Dominik Krug, Marc T. M. Koper

Understanding and manipulating gas bubble evolution during electrochemical water splitting is a crucial strategy for optimizing the electrode/electrolyte/gas bubble interface. Here gas bubble dynamics are investigated during the hydrogen evolution reaction on a well-defined platinum microelectrode by varying the electrolyte composition. We find that the microbubble coalescence efficiency follows the Hofmeister series of anions in the electrolyte. This dependency yields very different types of H₂ gas bubble evolution in different electrolytes, ranging from periodic detachment of a single H₂ gas bubble in sulfuric acid to aperiodic detachment of small H₂ gas bubbles in perchloric acid. Our results indicate that the solutal Marangoni convection, induced by the anion concentration gradient developing during the reaction, plays a critical role at practical current density conditions. The resulting Marangoni force on the H₂ gas bubble and the bubble departure diameter therefore depend on how surface tension varies with concentration for different electrolytes. This insight provides new avenues for controlling bubble dynamics during electrochemical gas bubble formation.

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Iris Burgers, Elena Pérez-Gallent, Earl Goetheer, Ruud Kortlever

Aqueous electrolytes are most commonly used for the CO₂ reduction reaction (CO₂RR), but suffer from a low CO₂ solubility that limits the reaction. Electrochemical CO₂ reduction in nonaqueous electrolytes can provide a solution, due to the higher CO₂ solubility of organic solvent-based electrolytes. Herein, the product distribution of the electrochemical CO₂ reduction on polycrystalline Cu in 0.7 m tetraethylammonium chloride in propylene carbonate with different water additions (0, 10, and 90 v%), and for different operating conditions (10, 25, 40, and 60 °C), is investigated. It is found that CO₂ reduction on Cu in a propylene carbonate solution results in H₂, CO, and formic acid formation only, even though Cu is known to produce C₂₊ products such as ethylene and ethanol in aqueous electrolytes. Increasing the operating temperature increases the CO₂RR kinetics and shows an improvement in CO formation and decrease in H₂ formation. However, increasing the operating temperature also increases water transport through the membrane, resulting in an increase of H₂ formation over time when operating at 60 °C.

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Onno van der Heijden, Dr. Sunghak Park, Jordy J. J. Eggebeen, Prof. Dr. Marc T. M. Koper

A large variety of nickel-based catalysts has been investigated for the oxygen evolution reaction (OER) in alkaline media. However, their reported activity, as well as Tafel slope values, vary greatly. To understand this variation, we studied electrodeposited Ni₈₀Fe₂₀OOH catalysts with different loadings at varying rotation rates, hydroxide concentrations, with or without sonication. We show that, at low current density (<5 mA cm⁻²), the Tafel slope value is ≈30 mV dec⁻¹ for Ni₈₀Fe₂₀OOH. At higher polarization, the Tafel slope continuously increases and is dependent on rotation rate, loading, hydroxide concentration and sonication. These Tafel slope values are convoluted by non-kinetic effects, such as bubbles, potential-dependent changes in ohmic resistance and (internal) OH⁻ gradients. As best practise, we suggest that Tafel slopes should be plotted vs. current or potential. In such a plot, it can be appreciated if there is a kinetic Tafel slope or if the observed Tafel slope is influenced by non-kinetic effects.

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Nynke van Uffelen

Energy justice often distinguishes between different tenets, such as distributive, procedural and recognition justice. Recognition justice has a distinct status compared to the other two as its meaning seems the least tangible to grasp. In this article, a systematic literature study was conducted to the definitions and interpretations of recognition justice, showing that the concept currently refers to a large variety of phenomena. This diversity obscures what “recognition justice” actually measures. This paper aims to revisit the concept of recognition justice in energy justice by asking the following question: what does the tenet of recognition justice refer to, taking into account the philosophical roots of the concept? To do so, key texts from Axel Honneth and Nancy Fraser were studied in-depth, resulting in four main insights: (1) there are two approaches to recognition justice; (2) actors can be (mis)recognised in multiple ways; (3) two different yet complementary methods for identifying instances of misrecognition can be distinguished; and (4) recognition justice cannot be reduced to other tenets of justice. These findings cumulate in a revisited definition of recognition justice as concerned with the adequate recognition of all actors through love, law, and status order. This definition structures the large variety of understandings in the scholarship, and it has the potential to provide a more fine-grained explanation of energy controversies, which advances the ultimate aim of making energy systems and policies more just.

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Ameya Ranade, Kaustub Singh, Alessandro Tamburini, Giorgio Micale, David A. Vermaas

Reverse electrodialysis (RED) is a technology to generate electricity from two streams with different salinities. While RED systems have been conventionally used for electricity generation, recent works explored combining RED for production of valuable gases. This work investigates the feasibility of producing hydrogen and chlorine in addition to electricity in an RED stack and identifies potential levers for improvement. A simplified one-dimensional model is adopted to assess the technical and economic feasibility of the process. We notice a strong disparity in typical current densities of RED fed with seawater and river water and that in typical water (or chlor-alkali) electrolysis. This can be partly mitigated by using brine and seawater as RED feeds. Considering such an RED system, we estimate a hydrogen production of 1.37 mol/(m² h) and an electrical power density of 1.19 W/m². Although this exceeds previously reported hydrogen production rates in combination with RED, the levelized costs of products are 1–2 orders of magnitude higher than the current market prices at the current state. The levelized costs of products are very sensitive to the membrane price and performance. Hence, going forward, manufacturing thinner and highly selective membranes is required to make the system competitive against the consolidated technologies.

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Richard P. van Leeuwen, Annelies E. Boerman, Edmund W. Schaefer, Gerwin Hoogsteen, Yashar S. Hajimolana

Recently, smart energy hubs with hydrogen conversion and storage have received increased attention in the Netherlands. The hydrogen is to be used for vehicle filling stations, industrial processes and heating. The scientific problem addressed in this paper is the proper sizing of capacities for renewable energy generation, hydrogen conversion and storage in relation to a feasible business case for the energy hub while achieving security of supply. Scenario analysis is often used during the early stages of the energy planning process, and for this an easy-to-use analysis model is required. This paper investigates available modelling approaches and develops an algorithmic modelling method which is worked out in Microsoft Excel and offers ease of use for scenario analysis purposes. The model is applied to case study, which leads to important insights such as the expected price of hydrogen and the proper sizing of electrolyser and hydrogen storage for that case. The model is made available open-source. Future work is proposed in the direction of application of the model for other project cases and comparison of results with other available modelling tools.