Effect of different alkali metal cations on the oxygen evolution activity and battery capacity of nickel electrodes in concentrated hydroxide electrolytes

The effect of different alkali metal cations on the oxygen evolution activity and battery capacity of nickel electrodes has recently been studied in low concentration alkali hydroxide electrolytes. As high concentration hydroxide electrolytes are favored in applications due to their high conductivity, we investigate if the cation effects observed in low concentration electrolytes translate to more industrially relevant conditions for both alkaline water electrolysis and nickel iron batteries. We investigate the alkali metal cation effect on the electrochemical properties of nickel electrodes in highly concentrated hydroxide electrolytes by adding Li+, Na+, Cs+ and Rb+ cations to a 6.5 M KOH electrolyte, while keeping the hydroxide concentration constant. For OER we find a trend in activity similar to that at low concentrations Rb+>Cs+>K+>Na+>Li+, where especially larger additions of Rb+ and Cs+ (1 M or 0.5 M) cause a significant decrease in OER potential. Smaller cations interact with the layered hydroxide structures in NiOOH to stabilize the α/γ phases and increase the potential for OER. The intercalation of small cations also causes an increase in battery electrode capacity because of the higher average valence of the Ni(OH)2/NiOOH α/γ pair. Small concentrations of Li+ added to a concentrated KOH electrolyte can therefore be beneficial for the nickel electrode battery functionality and for an integrated battery and electrolyser system, where it increases the battery capacity without a significant increase in OER onset potential.

A.Mangel Raventos, R.Kortlever

Operando isotope selective ammonia quantification in nitrogen reduction studies via gas chromatography-mass spectrometry

Rapid advances in electrocatalytic ammonia synthesis are impeded by laborious detection methods commonly used in the field and by constant risk of external contaminations, which generates misleading false positives. We developed a facile real-time GC-MS method for sensitive isotope NH3 quantification, requiring no external sample manipulations. This method ensures high detection reliability paramount to accelerate (electro-)catalyst screening.

Davide Ripepi, Riccardo Zaffaroni, Martin Kolen, Joost Middelkoop and Fokko M. Mulder

Polymer Modification of Surface Electronic Properties of Electrocatalysts

Finding alternative ways to tailor the electronic properties of a catalyst to actively and selectively drive reactions of interest has been a growing research topic in the field of electrochemistry. In this Letter, we investigate the tuning of the surface electronic properties of electrocatalysts via polymer modification. We show that when a nickel oxide water oxidation catalyst is coated with polytetrafluoroethylene, stable Ni–CFx bonds are introduced at the nickel oxide/polymer interface, resulting in shifting of the reaction selectivity away from the oxygen evolution reaction and toward hydrogen peroxide formation. It is shown that the electron-withdrawing character of the surface fluorocarbon molecule leaves a slight positive charge on the water oxidation intermediates at the adjacent active nickel sites, making their bonds weaker. The concept of modifying the surface electronic properties of an electrocatalyst via stable polymer modification offers an additional route to tune multipathway reactions in polymer/electrocatalyst environments, like with ionomer-modified catalysts or with membrane electrode assemblies.

Anirudh Venugopal, Laurentius H. T. Egberts, Jittima Meeprasert, Evgeny A. Pidko, Bernard Dam, Thomas Burdyny, Vivek Sinha, Wilson A. Smith

Surface Protolysis and Its Kinetics Impact the Electrical Double Layer

Surface conductivity in the electrical double layer (EDL) is known to be affected by proton hopping and diffusion at solid-liquid interfaces. Yet, the role of surface protolysis and its kinetics on the thermodynamic and transport properties of the EDL are usually ignored as physical models consider static surfaces. Here, using a novel molecular dynamics method mimicking surface protolysis, we unveil the impact of such chemical events on the system’s response. Protolysis is found to strongly affect the EDL and electrokinetic aspects with major changes in ζ potential and electro-osmotic flow.

Max F. Döpke, Fenna Westerbaan van der Meij, Benoit Coasne, and Remco Hartkamp

Development of a Conceptual Framework for Evaluating the Flexibility of Future Chemical Processes

Incorporating (operational) flexibility into process design has been a key approach to cope with uncertainties. The increasing penetration of renewables and the need for developing new low-carbon technologies will increase the demand for flexibility in chemical processes. This paper presents a state-of-the-art review focusing on the origin, definition, and elements of flexibility in the chemical engineering context. The article points out a significant overlap in terminology and concepts, making it difficult to understand and compare flexibility potential and constraints among studies. Further, the paper identifies a lack of available metrics for assessing specific types of flexibility and the need for developing indicators for exploring the potential flexibility of novel chemical processes. The paper proposes a classification of flexibility types and provides an overview of design strategies that have been adopted so far to enable different types of flexibility. Finally, it offers a conceptual framework that can support designers to evaluate specific types of flexibility in early-stage assessments of novel chemical processes.

Jisiwei Luo, Jonathan Moncada and Andrea Ramirez

Earlier Publications

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