Adds a tikz picture with an equivalent electrical circuit and the Nyquist plot for Randles circuit with CPE

electrochemical_OCP_EIS_LPR/EIS_insert.tex

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+\documentclass[tikz, border=5pt]{standalone}
+\usepackage[siunitx]{circuitikz} % Use circuitikz package
+\usetikzlibrary{arrows, decorations.markings} % Keep for main plot
+
+
+\begin{document}
+
+\def\cx{1.75}
+\def\cy{-0.25}
+
+\begin{tikzpicture}[
+  every node/.style={font=\scriptsize} % Make all annotations smaller
+]
+  \draw[->] (0, 0) -- (3.2, 0) node[right] {$Z'$};
+  \draw[->] (0, 0) -- (0, 1.2) node[above] {$-Z''$};
+
+  % Thick line above x axis with an arrow and text in the middle
+  \draw [thick,
+         decoration={markings, mark=at position 0.5 with {
+           \arrow{>}
+           \node[above=2pt] {$R_p || \textrm{CPE}$};
+           \node[below=0.5pt] {$\omega\!\uparrow$};
+         }},
+         postaction={decorate},
+         domain=15.25:164.75] plot
+         ({\cx+cos(\x)}, {\cy+sin(\x)});
+
+  % Dotted arc below x axis
+  \draw [thin,dashed, domain=-15.25:15.25] plot
+  ({\cx+cos(\x)}, {\cy+sin(\x)});
+
+  %% Dotted diameter below x axis
+  \draw[thin,dashed] ({\cx+cos(164.75)}, {\cy+sin(164.75)}) -- ({\cx+cos(-15.25)}, {\cy+sin(-15.25)});
+
+  % Show the influence of Rs
+  \draw[thin, dashed,->]  (0,0.07) -- ({\cx+cos(164.75)}, 0.07) node[midway, above] {$R_s$};
+
+  % --- Equivalent Electrical Circuit (using circuitikz) ---
+  \begin{scope}[xshift=3.65cm, yshift=0.5cm, transform shape]
+    \ctikzset{bipoles/length=0.3cm} % Adjust component size
+    \draw (0,0) to[R, o-, l_=$R_s$] (0.6,0) coordinate(junc); % Rs with start terminal
+    \draw (junc) -- ++(0.05,0) coordinate (junc2); % Junction wire
+    \draw (junc2) -- ++(0, 0.3) to[R, l=$R_p$] ++(0.8, 0) coordinate (rp_end); % Top branch
+    \draw (junc2) -- ++(0,-0.3) to[C, l_=CPE] ++(0.8, 0) coordinate (cpe_end); % Bottom branch
+    \draw (rp_end) -- (rp_end |- cpe_end); % Closing vertical wire
+    \draw (rp_end |- junc2) to[short, -o] ++(0.2,0); % Add terminal endpoint wire
+  \end{scope}
+
+  
+\end{tikzpicture}
+\end{document}