# Electrochemical Ion Pumping Device for Blue Energy Recovery: Mixing Entropy Battery
## 7 Conclusions and Outlooks  
Salinity gradient energy or blue energy using MEBs is clearly a plausible alternative to renewable energy around the world. In comparison with classical marine energies based on the mechanical action of waves and coastal wind, the blue energy presents interesting advantages related to reduced installation and material costs and corrosion protection requirements in coastal areas. However the working conditions in coastal areas pose a challenge for an MEB installation to overcome long term exposure to humidity with high salinity, wave action, splash and high corrosive stress, which together give rise to very fast corrosion in important sectors of a plant, increasing, as a result, the cost of this alternative energy harvesting [67]. The latest developments in this area, towards new and more efficient blue energy devices, encourage new ideas for the development of environmentally friendly projects. While blue energy is closely related to the recovery of chemical energy from the mixture of seawater and the river water that flows into the sea, it is also true that it is possible to consider other alternatives, such as the following:  
1. Synthetic or natural saline solutions such as aliphatic brines in South America can serve as electrolytes in areas where no rivers with considerable flows are available. This alternative opens the possibility for this technology to be used in nearby coastal areas, or high altitude salt lake brines, as is the case for many altiplanic places in South America. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Ref.** & **Anode Material** & **Covering Method** & **Material [\%]** & **Substrate** & **Electrode Mass [mg/cm\({}^{2}\)]** \\ \hline
[5] & Ag & Drop Casting & 85 & Carbon Cloth & 40 \\
[22] & Ag & Ink Coating & 85 & Carbon Cloth & 10 \\
[1] & Ag & Ag Foil & 100 & - & - \\
[23] & Ag & Ag Sheet & 100 & Cu-CPE & - \\
[13] & BiOCl & Spread & 80 & Carbon Paper & 4.8 \\
[39] & PPy/Ag & Electropolymerization & - & ITO & - \\ \hline \end{tabular}
\end{table} 
Table 6: Anode material used in MEB. Figure 10: Structure of Polypyrrole for respective redox states. Illustration based from [65]. 2. Another possibility would be to consider rejection flows from reverse osmosis plants as concentrated NaCl solution and seawater as the diluted solution in arid places where there are no rivers or treatment plants that flow into the sea. 3. It is interesting to note that fresh water availability, which is the main restrictive factor to implement MEB technologies in arid places, can be overcome by using solar energy to obtain distilled water with complete recycling of the electrolyte to achieve conversion of solar energy into electrical energy. The solar distillation technologies are well known and have a historical record of applications in Northern Chile as far back as 1842 and worked effectively for 40 years [68]. This fresh water collection alternative would make harvesting energy from salinity gradient possible at lower costs and greater efficiency. 4. The use of wastewater effluents as a source of fresh water could be useful for obtaining electrical energy through MEBs. However, more research related to the behavior of electrodes in the presence of biological contaminants and free chlorine is needed. Today the efforts of many researchers are focused on the search for new cathode materials capable of storing the greatest amount of energy with good reversibility as well as low over-potentials and the lowest self-shocks or electrical leaks. This condition enables a good response under high intensity charging and discharging cycles, in addition to lower operational costs that overall fulfill a requirement for an environmentally friendly technology.