# Electrosynthesis of HKUST-1 with Flow-Reactor Post-Processing
## 1 Introduction  
Metal-organic frameworks (MOFs) are crystalline materials comprised of metal ions connected via coordination bonds with organic linkers. The diversity of metal ions and organic linkers available for use as building blocks have resulted in the creation of thousands of MOFs with a broad range of characteristics. In particular, the high surface area of certain MOFs has encouraged research in gas adsorption and fuel storage applications [1, 2]. Despite a large number of reported MOFs very few have been successfully commercialised, due in part to the small scales of most synthetic methods [3]. It is beyond the scope of this work to present a comprehensive summary of MOFs synthesis methods and the reader is directed towards the existing review papers [4, 5, 6, 7, 8].  
Recent work has demonstrated that continuous flow synthesis is a promising method for increasing the scale of MOFs production while maintaining product quality [9, 10]. In comparison to a typical reaction vessel, continuous flow reactors offer a higher ratio of surface area to volume and the enhanced scalability of this ratio is beneficial for improving synthetic yields. Parameters such as reactor temperature, flow rate, and retention time can be adjusted to customise the properties of the desired MOFs. Other advantages of this methodology include its efficient heat and mass transfer; relatively fast synthesis time; and modularity, allowing for the incorporation of additional treatments or analysis. However, as metal salts are usually used as starting materials the metal's counter-ion can form various waste products which must be disposed of, and on large scales, it can take days to wash this waste off the product.  
In 2005 BASF patented an electrochemical method for MOFs synthesis which uses electrodes as a source of metal ions [11]. Anodic dissolution works by electrochemically oxidising an electrode made of the desired metal as it is submerged in a solution containing the other reactants [5]. As metal salts can be avoided this method is cleaner than other techniques; however, adding an electrolyte is typically required to improve the conductivity of the solution [12; 13]. Reaction conditions such as current density, electrolyte, and solution conductivity offer additional forms of control over other synthetic techniques. In addition to bulk synthesis, this method can also be used to prepare MOFs layers on conductive substrates [14]. Electrochemical synthesis is faster than solvothermal and slow diffusion methods, requires less solvent, and can be operated continuously; however, to date, only a small number of MOFs have been electrochemically synthesised. Prevention of electrode passivation is a challenge when performing electrosynthesis on long time scales, however, this can be resolved by intermittent polarity reversal of the electrodes [15].  
HKUST-1, or [CuI\({}_{3}\)(BTC)\({}_{2}\)] where H\({}_{3}\)BTC = benzene-1,3,5-tricarboxylic acid, was first reported in 1999 [16]. Originally synthesised solvothermally, HKUST-1 has since been widely studied for its gas adsorption qualities [2], and potential applications in separations and heterogeneous catalysis [17; 18]. HKUST-1 has now been synthesised using a range of methodologies including mechanochemically [19], continuous flow [10; 20], and electrochemically [16]; the latter of these methods being used in the production of commercial HKUST-1 known as BasoliteTM C300. This paper is the first published research where the combination of electrochemical MOFs synthesis with continuous flow chemistry is investigated. The research aims to produce a scalable synthesis method that produces high-quality MOFs without additional electrolyte or washing.