# Practical Methodology for a Three-Dimensional-Printed Hybrid Desalination System
## 1 Introduction
(2017), involve independent RED and ED reactors, where RED acts as a pre-desalination step or an energy donor for the ED process [15; 16]. Their findings demonstrated the system's feasibility, achieving  
Figure 1: RED and ED cells: (**a**) diagram of a RED unit cell; (**b**) diagram of an ED unit cell. desalinated water conductivity as low as 72 uS/cm, suitable for human consumption [16]. While these systems are feasible, they suffer from low energy efficiency due to converting chemical and electrical energy. Internally integrated systems, such as the one introduced by [PERSON] et al. (2015), couple RED and ED within a single reactor, using the salinity gradient energy from seawater and brine to drive the ED process directly. This system produced 48.3 L of fresh water (\(\sim\)420 mg/L) daily, consuming 229.4 L of brine and 132.8 L of seawater [17]. In an internally integrated hybrid system, the desalination process is directly powered by ion flow, minimizing energy losses from conversion processes. Furthermore, RED/ED systems only require a single pair of electrodes, whereas external integrations use two pairs. However, the performance of internally integrated RED/ED reactors is influenced by numerous factors, such as electrolyte concentration, the number of unit cells, and the thickness of the solution compartments [18]. Hybrid RED-ED systems can utilize the residual brine from ED, a byproduct of desalination, to generate energy through RED. Furthermore, the modularity of RED and ED reactors facilitates the system scale-up. The study of desalination systems and devices, such as RED and ED, at the laboratory level is essential for advancing their development. Three-dimensional printing enables the creation of customized devices that optimize the design of these reactors. This technology not only facilitates research but also makes the development of tailored prototypes more accessible, bridging the gap between experimental research and the practical implementation of desalination solutions. Since its inception in the 1980s, 3D printing, also known as additive manufacturing, has gained widespread popularity across various industries and research fields due to its remarkable versatility in producing an endless array of three-dimensional models using innovative materials. While the application of 3D printing in the fabrication of electrochemical reactors is still in its early developmental phase [19], a growing body of research has already explored its potential in areas such as energy generation [20], desalination [21], batteries [22], biosensors [23], electrode manufacturing [24], and electrochemical sensing devices [25]. Additive manufacturing presents significant advantages for the design and development of RED/ED systems, as it enables the fabrication of intricate geometries that improve the hydrodynamic performance and overall efficiency of the system [26]. Despite these advancements, most studies have focused on 3D printing individual components of reactors. To date, a comprehensive methodology that integrates the design, fabrication, and electrochemical characterization of a laboratory-scale RED-ED desalination system has not been reported. Addressing the multidisciplinary interactions between processes, materials, and structural components is fundamental to driving the ongoing development and improvement of these systems. The use of 3D printing can significantly speed up the development of RED/ED reactors, particularly during the early stages, by enabling the rapid fabrication of laboratory-scale prototypes tailored to precise design and geometry specifications. Additionally, it allows for easy adjustments to various parameters, facilitating future scalability for full-scale applications or industrial use. In-house production of these reactors not only offers the flexibility to customize designs to meet specific requirements but also helps reduce both costs and production times.