# Electrochemical Ion Pumping Device for Blue Energy Recovery: Mixing Entropy Battery
## 6 Anode Materials Used in MEB
### Silver  
Silver (_Ag_) electrodes are the most popular anodic electrodes [13] used in MEBs because of their reversibility and adaptability features in the presence of \(Cl^{-}\) ions. The reason is that the anodic _AgCl_ phase formation can take in an electrochemical window devoid of oxygen evolution reaction [55].  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Ref.**} & **Active** & \multirow{2}{*}{**Synthesis Method**} & **Covering** & **Active** & \multirow{2}{*}{**Substrate**} & **Electrode** \\  & **Material** & & & **Method** & **Material [\%]** & & **Mass** \\ \hline
[5] & LiFePO\({}_{4}\) & Polymeric Synthesis & Drop Casting & 80 & Carbon Cloth & 25 \\
[22] & Na\({}_{4}\)Mn\({}_{5}\)O\({}_{18}\) & Solid State Reaction & Ink Coating & 85 & Carbon Cloth & 14 \\
[1] & Na\({}_{2}\)Mn\({}_{5}\)O\({}_{10}\) & Pachini Method & Doctor Blade & 80 & Graphite & 8 \\
[7] & MnO\({}_{2}\) & Co-Precipitation & Doctor Blade & 70 & Graphite Sheet & 34 \\
[11] & CuHCF & Dropwise & Spread & 90 & Carbon Plate & 5 \\
[7] & CuHCF & Co-Precipitation & Doctor Blade & 70 & Graphite Sheet & - \\
[8] & CuHCF & Co-Precipitation & Doctor Blade & 70 & Graphite Foil & 4.4 \\
[13] & CuHCF & Co-Precipitation & Spread & 80 & Carbon Paper & 4.8 \\
[23] & CoHCF & Co-Precipitation & Electrodeposition & - & CPE & 0.193 \\
[39] & NiHCF & Co-Precipitation & Hand Painting & 80 & Carbon Cloth & - \\ \hline \hline \end{tabular}
\end{table}
Table 4: Preparation of battery material and PBA for cathodes in MEBs.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Ref.**} & **Active** & \multicolumn{2}{c}{**Relevant Characteristics**} & \multicolumn{2}{c}{**Revestible**} & **Efficiency** & **Blue Energy** \\ \cline{2-6}  & **Material** & **Advantage** & **Disadvantage** & **Capacity [mAu/gl]** & **[\%]** & **Recovery** \\ \hline
[5] & LiFePO\({}_{4}\) & High Stability & Poor E.C & 120 & - & 13.5 \(\mu\)W/cm\({}^{2}\) \\
[22] & Na\({}_{4}\)Mn\({}_{5}\)O\({}_{18}\) & High Capacity Retention & Low Charge Capacity & 113 & 68 & 0.65 kW/m\({}^{3}\) \\
[5] & Na\({}_{2}\)Mn\({}_{5}\)O\({}_{10}\) & High Surface Area & Low Charge Capacity & - & 75 & 10.5 \(\mu\)W/cm\({}^{2}\) \\
[11] & CuHCF & & - & 69 & 13900 \(\mu\)W/cm\({}^{2}\) \\
[7] & CuHCF & High Capacity & High Irreversible Reaction & - & - & 411 mW/m\({}^{2}\) \\
[8] & CuHCF & & - & - & 6.3 mW/m\({}^{2}\) \\
[13] & CuHCF & & - & - & 87 mW/m\({}^{2}\) \\
[23] & CoHCF & High Energy Density & Cell Voltage Limited (<1 V) & 130 & 65 & 4632 \(\mu\)W/cm\({}^{2}\) \\
[39] & NiHCF & Efficient Energy Consumption & Low water recovery & 60 & - & 16.8 kJ/mol \\ \hline \hline \end{tabular}
\end{table}
Table 5: Blue energy recovery using different cathode materials.  
Unfortunately, _AgCl_ phase formation takes place through many different forms of parallel reactions, as follows:  
\[Ag+nCl^{-}\leftrightarrow AgCl_{n+1}^{n-}+e^{-} \tag{49}\]  
The typical anodic reactions \(n=1\) (\(n=1,2,3\)) with thermodynamic stabilities [56] take place according to the following equations [54; 55; 22; 27; 28; 56; 5]:  
\[Ag+Cl^{-}\leftrightarrow AgCl+e^{-}\ E_{Ag/AgCl}^{0}=220\ [mV] \tag{50}\]  
The most relevant reactions and their equilibrium constants are [22]  
\[Ag^{+}+Cl^{-}\leftrightarrow AgCl_{(S)},\ \big{[}Ag^{+}\big{]}[Cl^{-}]=1.8 \cdot 10