68

Hello I wanted to draw a Hofmann voltameter in TikZ like in this image:

enter image description here

Unfortunately, there are a lot of curves and shapes that are tedious to draw. Is there an easy way to draw it or do I have to settle for something like this

\begin{tikzpicture}[xscale=0.7]
\filldraw[black!50!white] (0,0)  to[line to] (0,4.5) to[line to] (2,4.5) to[line to] (2,2) to[line to] (4,2) to[line to] (4,5) to[line to] (6,5) to[line to] (6,2) to[line to] (8,2) to[line to] (8,3) to[line to] (10,3) to[line to] (10,0) to[line to] (8,0) to[line to] (8,1) to[line to] (2,1) to[line to] (2,0) to[line to] (0,0);
\node (Anode) at (-0.8,0.3) {Anode};
\node (Cathode) at (11,0.3) {Cathode};
\draw[line width=1pt] (1,0) to[line to] (1,-0.5)  to[line to] (4.7,-0.5);
\draw[line width=1pt] (5.3,-0.5) to[line to] (9,-0.5) to[line to] (9,0);
\draw[line width=1pt] (4.7,-1)  to[line to] (4.7,0);
\draw[line width=1pt] (5.3,-0.7) to[line to] (5.3,-0.3);
\fill[black!20!white] (0,0)  to[line to] (0,4.5) to[line to] (2,4.5) to[line to] (2,2) to[line to] (4,2) to[line to] (4,5) to[line to] (6,5) to[line to] (6,2) to[line to] (8,2) to[line to] (8,3) to[line to] (10,3) to[line to] (10,0) to[line to] (8,0) to[line to] (8,1) to[line to] (2,1) to[line to] (2,0) to[line to] (0,0);
\fill[black!100!white] (0.875,0) rectangle (1.125,0.7);
\fill[black!100!white] (8.875,0) rectangle (9.125,0.7);
\draw[line width=1pt] (0,0) to[line to] (0,6) to[line to] (2,6) to[line to] (2,2) to[line to] (4,2) to[line to] (4,7) to[line to] (6,7) to[line to] (6,2) to[line to] (8,2) to[line to] (8,6) to[line to] (10,6) to[line to] (10,0) to[line to] (8,0) to[line to] (8,1) to[line to] (2,1) to[line to] (2,0) to[line to] (0,0);
\end{tikzpicture}

Which yields this:

enter image description here

  • For the electrical devices there is the circuit.ee.IEC library which comes with TikZ (screenshot from the manual). – Henri Menke Jul 17 '18 at 5:08
  • I believe the circuit iee iec tikz package does not come with a voltameter in it (correct me if I'm wrong) so I would presume the only way to draw it is using lines and shapes. I'm not worried about the circuit at the bottom of the picture it's the apparatus I'm struggling with. – sab hoque Jul 17 '18 at 5:24
  • 2
    You could draw the round elements with the to[in=...,out=...] and/or arcs, but yes, it will be some effort. – user121799 Jul 17 '18 at 6:11
173
+550

To answer your question: No, there is not an easy way to draw this, other than to try some vectorisation on the .png (e.g. with Autotracer.org). Fortunately, some of us don't have anything better to do :)

Edit
Fixed the left and right tubes, noticed that they are supposed to be open at the top.

Edit 2
I wanted to draw the pattern of the acidulated water too, so now the image is complete :) . Of course you can choose for yourself which one you like better, I just wanted to give you that choice.

enter image description here

New code:

\documentclass[tikz,margin=2mm]{standalone}

\usepackage{tikz}
\usetikzlibrary{decorations.pathreplacing,shapes,patterns,calc}

\makeatletter
\tikzset{
    horizontal dashes length/.store in=\@hordash@length,
    horizontal dashes distance/.store in=\@hordash@dist,
    horizontal dashes line width/.store in=\@hordash@lw,
    horizontal dashes length=5pt,
    horizontal dashes distance=2pt,
    horizontal dashes line width=0.2pt,
}

\pgfdeclarepatternformonly[\@hordash@length,\@hordash@dist,\@hordash@lw]{horizontal dashes}
{\pgfpointorigin}
{\pgfpoint{\@hordash@length+\@hordash@dist}{2*\@hordash@dist}}
{\pgfpoint{\@hordash@length+\@hordash@dist}{2*\@hordash@dist}}
{
    \pgfpathmoveto{\pgfpoint{0.5*\@hordash@dist}{1.5*\@hordash@dist}}
    \pgfpathlineto{\pgfpoint{0.5*\@hordash@dist+\@hordash@length}{1.5*\@hordash@dist}}
    \pgfpathmoveto{\pgfpoint{0mm}{0.5*\@hordash@dist}}
    \pgfpathlineto{\pgfpoint{0.5*\@hordash@length}{0.5*\@hordash@dist}}
    \pgfpathmoveto{\pgfpoint{\@hordash@dist+0.5*\@hordash@length}{0.5*\@hordash@dist}}
    \pgfpathlineto{\pgfpoint{\@hordash@dist+\@hordash@length}{0.5*\@hordash@dist}}
    \pgfsetlinewidth{\@hordash@lw}
    \pgfusepath{stroke}
}
\makeatother

\begin{document}
    \begin{tikzpicture}[
        thick,
        >=latex,
        line join=round,
        ode/.style={
            minimum width=2mm,
            minimum height=7mm,
            draw,
            fill=white,
            postaction={
                pattern = crosshatch dots
            }
        },
        cork/.style={
            minimum width=4mm-2\pgflinewidth,
            minimum height=6mm,
            draw,
            fill=white,
            postaction={
                pattern = north east lines
            }
        },
        battery/.style={
            minimum width=6mm+2pt,
            minimum height=8mm,
            outer sep=0pt,
            node contents={},
            path picture={
                \draw[line width=1pt] (-3mm-0.5pt,-4mm) -- ++(0,8mm);
                \draw[line width=3pt] (-1mm-0.5pt,-2mm) -- ++(0,4mm);
                \draw[line width=1pt] (1mm-0.5pt,-4mm) -- ++(0,8mm);
                \draw[line width=3pt] (3mm-0.5pt,-2mm) -- ++(0,4mm);
            },
        },
        amperemeter/.style={
            draw,
            circle,
            minimum size=10mm,
            node contents={\( A \)},
        },
    ]

        \filldraw[pattern=horizontal dashes,line width=0.4pt] (0,-0.2)
            -- ++(-1,0) 
            -- ++(0,-0.4) -- ++ (-0.4,0) -- ++(0,4.65) 
            arc (180:270:0.1) -- ++(0.2,0) arc (270:360:0.1) 
            -- ++(0,-3.85) -- ++(0.8,0) -- ++(0,7.7)
            .. controls +(0,0.4) and +(0,-0.9) .. ++(-0.8,1.25)
            arc (180:270:0.1)
            let \p1 = ++(0,0) in --(-\x1,\y1)
            arc (270:360:0.1)
            .. controls +(0,-0.9) and +(0,0.4) .. ++(-0.8,-1.25)
            -- ++(0,-7.7) -- ++(0.8,0)  -- ++(0,1)
            arc (180:270:0.1) -- ++(0.2,0) arc (270:360:0.1)
            -- ++(0,-1.8) -- ++(-0.4,0) -- ++(0,0.4)
            -- cycle;
        \draw (0,-0.2)
            -- ++(-1,0) -- ++(0,-0.8) -- ++(0.1,-0.1) 
            ++ (-0.6,0) -- ++(0.1,0.1) -- ++(0,7.25)
            .. controls +(0,0.2) and +(0,-0.1) .. ++(0.16,0.3)
            .. controls +(0,0.45) and +(0,-0.22) .. ++(0.02,1.25)
            ++(0.04,0)
            .. controls +(0,-0.22) and +(0,0.45) .. ++(0.02,-1.25)
            .. controls +(0,-0.1) and +(0,0.2) .. ++(0.16,-0.3)
            -- ++(0,-6.05) -- ++(0.8,0) -- ++(0,7.7)
            .. controls +(0,0.4) and +(0,-0.9) .. ++(-0.8,1.25)
            .. controls +(0,0.4) and +(0,-0.3) .. ++(0.8,0.65)
            .. controls +(0,0.1) and +(0,0) .. ++(-0.1,0.1)
            let \p1 = ++(0,0) in (-\x1,\y1)
            .. controls +(0,0) and +(0,0.1) .. ++(-0.1,-0.1)
            .. controls +(0,-0.3) and +(0,0.4) .. ++(0.8,-0.65)
            .. controls +(0,-0.9) and +(0,0.4) .. ++(-0.8,-1.25)
            -- ++(0,-7.7) -- ++(0.8,0) -- ++(0,6.05)
            .. controls +(0,0.2) and +(0,-0.1) .. ++(0.16,0.3)
            .. controls +(0,0.45) and +(0,-0.22) .. ++(0.02,1.25)
            ++(0.04,0)
            .. controls +(0,-0.22) and +(0,0.45) .. ++(0.02,-1.25)
            .. controls +(0,-0.1) and +(0,0.2) .. ++(0.16,-0.3)
            -- ++(0,-7.25) -- ++(0.1,-0.1) ++ (-0.6,0)
            -- ++(0.1,0.1) -- ++(0,0.8) -- ++(-1,0);


        \node[ode,pin={[align=center]left:Anode\\\( + \)}] at (-1.2,0) (anode) {};
        \node[ode,pin={[align=center]right:Cathode\\\( - \)}] at (1.2,0) (cathode) {};

        \coordinate[pin={left:Oxygen}] (ox) at (-1.2,4.7);
        \coordinate[pin={right:Hydrogen}] (hy) at (1.2,5.1);
        \coordinate[pin={[pin distance=2.5cm,align=center]right:Acidulated\\water}] (aw) at (0.2,8.6);

        \node[cork] at (-1.2,-0.9) {};
        \node[cork] at (1.2,-0.9) {};

        \begin{scope}[shift={(1.2,6.8)},fill=white]
            \filldraw (0.45,-0.05) rectangle (0,0.05);
            \filldraw[fill=white,rounded corners=1pt] (-0.3,-0.15) rectangle ++(0.6,0.3);
            \filldraw[fill=white] (0.45,0) circle (0.075 and 0.2);
            \filldraw[fill=white] (0,0) circle (0.075);
        \end{scope}
        \begin{scope}[xscale=-1,shift={(1.2,6.8)},fill=white]
            \filldraw (0.45,-0.05) rectangle (0,0.05);
            \filldraw[fill=white,rounded corners=1pt] (-0.3,-0.15) rectangle ++(0.6,0.3);
            \filldraw[fill=white] (0.45,0) circle (0.075 and 0.2);
            \filldraw[fill=white] (0,0) circle (0.075);
        \end{scope}

        \node (bat) at (-0.5,-3) [battery];
        \node (amp) at (1,-3) [amperemeter];
        \node (res) at (3,-3) [draw,minimum width=15mm,minimum height=2.5mm]{};

        \draw (anode) |- (bat);
        \draw (bat) -- (amp);
        \draw (amp) -- (res);
        \draw[->] (cathode) -- (cathode|-0,-1.5) -| (res.40);
    \end{tikzpicture}
\end{document} 

enter image description here

Old code:

\documentclass[tikz,margin=2mm]{standalone}

\usepackage{tikz}
\usetikzlibrary{decorations.pathreplacing,shapes,patterns,calc}

\begin{document}
    \begin{tikzpicture}[
        thick,
        >=latex,
        line join=round,
        ode/.style={
            minimum width=2mm,
            minimum height=7mm,
            draw,
            fill=white,
            postaction={
                pattern = crosshatch dots
            }
        },
        cork/.style={
            minimum width=4mm-2\pgflinewidth,
            minimum height=6mm,
            draw,
            fill=white,
            postaction={
                pattern = north east lines
            }
        },
        battery/.style={
            minimum width=6mm+2pt,
            minimum height=8mm,
            outer sep=0pt,
            node contents={},
            path picture={
                \draw[line width=1pt] (-3mm-0.5pt,-4mm) -- ++(0,8mm);
                \draw[line width=3pt] (-1mm-0.5pt,-2mm) -- ++(0,4mm);
                \draw[line width=1pt] (1mm-0.5pt,-4mm) -- ++(0,8mm);
                \draw[line width=3pt] (3mm-0.5pt,-2mm) -- ++(0,4mm);
            },
        },
        amperemeter/.style={
            draw,
            circle,
            minimum size=10mm,
            node contents={\( A \)},
        },
    ]

        \fill[white!80!black] (0,-0.2)
            -- ++(-1,0) 
            -- ++(0,-0.4) -- ++ (-0.4,0) -- ++(0,4.65) 
            arc (180:270:0.1) -- ++(0.2,0) arc (270:360:0.1) 
            -- ++(0,-3.85) -- ++(0.8,0) -- ++(0,7.7)
            .. controls +(0,0.4) and +(0,-0.9) .. ++(-0.8,1.25)
            arc (180:270:0.1)
            let \p1 = ++(0,0) in --(-\x1,\y1)
            arc (270:360:0.1)
            .. controls +(0,-0.9) and +(0,0.4) .. ++(-0.8,-1.25)
            -- ++(0,-7.7) -- ++(0.8,0)  -- ++(0,1)
            arc (180:270:0.1) -- ++(0.2,0) arc (270:360:0.1)
            -- ++(0,-1.8) -- ++(-0.4,0) -- ++(0,0.4)
            -- cycle;
        \draw (0,-0.2)
            -- ++(-1,0) -- ++(0,-0.8) -- ++(0.1,-0.1) 
            ++ (-0.6,0) -- ++(0.1,0.1) -- ++(0,7.25)
            .. controls +(0,0.2) and +(0,-0.1) .. ++(0.16,0.3)
            .. controls +(0,0.45) and +(0,-0.22) .. ++(0.02,1.25)
            ++(0.04,0)
            .. controls +(0,-0.22) and +(0,0.45) .. ++(0.02,-1.25)
            .. controls +(0,-0.1) and +(0,0.2) .. ++(0.16,-0.3)
            -- ++(0,-6.05) -- ++(0.8,0) -- ++(0,7.7)
            .. controls +(0,0.4) and +(0,-0.9) .. ++(-0.8,1.25)
            .. controls +(0,0.4) and +(0,-0.3) .. ++(0.8,0.65)
            .. controls +(0,0.1) and +(0,0) .. ++(-0.1,0.1)
            let \p1 = ++(0,0) in (-\x1,\y1)
            .. controls +(0,0) and +(0,0.1) .. ++(-0.1,-0.1)
            .. controls +(0,-0.3) and +(0,0.4) .. ++(0.8,-0.65)
            .. controls +(0,-0.9) and +(0,0.4) .. ++(-0.8,-1.25)
            -- ++(0,-7.7) -- ++(0.8,0) -- ++(0,6.05)
            .. controls +(0,0.2) and +(0,-0.1) .. ++(0.16,0.3)
            .. controls +(0,0.45) and +(0,-0.22) .. ++(0.02,1.25)
            ++(0.04,0)
            .. controls +(0,-0.22) and +(0,0.45) .. ++(0.02,-1.25)
            .. controls +(0,-0.1) and +(0,0.2) .. ++(0.16,-0.3)
            -- ++(0,-7.25) -- ++(0.1,-0.1) ++ (-0.6,0)
            -- ++(0.1,0.1) -- ++(0,0.8) -- ++(-1,0);


        \node[ode,pin={[align=center]left:Anode\\\( + \)}] at (-1.2,0) (anode) {};
        \node[ode,pin={[align=center]right:Cathode\\\( - \)}] at (1.2,0) (cathode) {};

        \coordinate[pin={left:Oxygen}] (ox) at (-1.2,4.7);
        \coordinate[pin={right:Hydrogen}] (hy) at (1.2,5.1);
        \coordinate[pin={[pin distance=2.5cm,align=center]right:Acidulated\\water}] (aw) at (0.2,8.6);

        \node[cork] at (-1.2,-0.9) {};
        \node[cork] at (1.2,-0.9) {};

        \begin{scope}[shift={(1.2,6.8)},fill=white]
            \filldraw (0.45,-0.05) rectangle (0,0.05);
            \filldraw[fill=white,rounded corners=1pt] (-0.3,-0.15) rectangle ++(0.6,0.3);
            \filldraw[fill=white] (0.45,0) circle (0.075 and 0.2);
            \filldraw[fill=white] (0,0) circle (0.075);
        \end{scope}
        \begin{scope}[xscale=-1,shift={(1.2,6.8)},fill=white]
            \filldraw (0.45,-0.05) rectangle (0,0.05);
            \filldraw[fill=white,rounded corners=1pt] (-0.3,-0.15) rectangle ++(0.6,0.3);
            \filldraw[fill=white] (0.45,0) circle (0.075 and 0.2);
            \filldraw[fill=white] (0,0) circle (0.075);
        \end{scope}

        \node (bat) at (-0.5,-3) [battery];
        \node (amp) at (1,-3) [amperemeter];
        \node (res) at (3,-3) [draw,minimum width=15mm,minimum height=2.5mm]{};

        \draw (anode) |- (bat);
        \draw (bat) -- (amp);
        \draw (amp) -- (res);
        \draw[->] (cathode) -- (cathode|-0,-1.5) -| (res.40);
    \end{tikzpicture}
\end{document} 
  • 1
    very nice; why doesn't it compile in lualatex? (it works fine with pdflatex) – JPi Jul 17 '18 at 15:18
  • 8
    I like the statement "Fortunately, some of us don't have anything better to do". That is the real Tikz spirit. There are alternatives, like drawing the device in Inkscape, save as SVG and convert the SVG to Tikz. (github.com/kjellmf/svg2tikz) But that is clearly inferior to this answer, far inferior to to real drawing in Tikz. Although we know Tikz is not a drawing program :) – jlinkels Jul 17 '18 at 20:05
  • 12
    @sabhoque if you publish something with this figure included, you could consider acknowledging the help in a footnote or something. – henning Jul 18 '18 at 11:26
  • 2
    @Max Snippe: it could be, maybe in a later version than what I have. Running a quick check on that makes me thing that "save as Tikz" is the process I described as svg2tikz but then integrated in Inkscape. Inkscape does have an option to save as Latex, which converts the drawing to PDF which integrates very nicely with your document. But it is raster, not vector. I should look into the Save as Tikz a bit deeper soon. – jlinkels Jul 19 '18 at 11:49
  • 2
    Damn, you even got the menisci... – DividedByZero Jul 20 '18 at 3:33
41

Final tikz image, big shoutout to Max Snippe (uses tikz package and mhchem package)

\begin{tikzpicture}[         
thick,         
>=latex,         
line join=round,         
ode/.style={             
    minimum width=2mm,             
    minimum height=7mm,             
    draw,             
    fill=white,             
    postaction={                 
        pattern = crosshatch dots             
    }         
},         
cork/.style={             
    minimum width=4mm-2\pgflinewidth,             
    minimum height=6mm,             
    draw,             
    fill=white,             
    postaction={                 
        pattern = north east lines             
    }         
},         
battery/.style={             
    minimum width=6mm+2pt,             
    minimum height=8mm,             
    outer sep=0pt,             
    node contents={},             
    path picture={                 
        \draw[line width=1pt] (-3mm-0.5pt,-4mm) -- ++(0,8mm);                 
        \draw[line width=3pt] (-1mm-0.5pt,-2mm) -- ++(0,4mm);                 
        \draw[line width=1pt] (1mm-0.5pt,-4mm) -- ++(0,8mm);                 
        \draw[line width=3pt] (3mm-0.5pt,-2mm) -- ++(0,4mm);             
    },         
},         
amperemeter/.style={             
    draw,             
    circle,             
    minimum size=10mm,             
    node contents={\( A \)},         
    },     
]
    \fill[white!80!black] (0,-0.2)             
        -- ++(-1,0)              
        -- ++(0,-0.4) -- ++ (-0.4,0) -- ++(0,4.65)              
        arc (180:270:0.1) -- ++(0.2,0) arc (270:360:0.1)              
        -- ++(0,-3.85) -- ++(0.8,0) -- ++(0,7.7)             
        .. controls +(0,0.4) and +(0,-0.9) .. ++(-0.8,1.25)             
        arc (180:270:0.1)             
        let \p1 = ++(0,0) in --(-\x1,\y1)             
        arc (270:360:0.1)             
        .. controls +(0,-0.9) and +(0,0.4) .. ++(-0.8,-1.25)             
        -- ++(0,-7.7) -- ++(0.8,0)  -- ++(0,1)             
        arc (180:270:0.1) -- ++(0.2,0) arc (270:360:0.1)             
        -- ++(0,-1.8) -- ++(-0.4,0) -- ++(0,0.4)             
        -- cycle;         
\draw (0,-0.2)             
    -- ++(-1,0) -- ++(0,-0.8) -- ++(0.1,-0.1)              
    ++ (-0.6,0) -- ++(0.1,0.1) -- ++(0,7.25)             
    .. controls +(0,0.2) and +(0,-0.1) .. ++(0.16,0.3)             
    .. controls +(0,0.45) and +(0,-0.22) .. ++(0.02,1.25)             
    ++(0.04,0)             
    .. controls +(0,-0.22) and +(0,0.45) .. ++(0.02,-1.25)             
    .. controls +(0,-0.1) and +(0,0.2) .. ++(0.16,-0.3)             
    -- ++(0,-6.05) -- ++(0.8,0) -- ++(0,7.7)             
    .. controls +(0,0.4) and +(0,-0.9) .. ++(-0.8,1.25)             
    .. controls +(0,0.4) and +(0,-0.3) .. ++(0.8,0.65)             
    .. controls +(0,0.1) and +(0,0) .. ++(-0.1,0.1)             
    let \p1 = ++(0,0) in (-\x1,\y1)             
    .. controls +(0,0) and +(0,0.1) .. ++(-0.1,-0.1)             
    .. controls +(0,-0.3) and +(0,0.4) .. ++(0.8,-0.65)             
    .. controls +(0,-0.9) and +(0,0.4) .. ++(-0.8,-1.25)             
    -- ++(0,-7.7) -- ++(0.8,0) -- ++(0,6.05)             
    .. controls +(0,0.2) and +(0,-0.1) .. ++(0.16,0.3)             
    .. controls +(0,0.45) and +(0,-0.22) .. ++(0.02,1.25)             
    ++(0.04,0)             
    .. controls +(0,-0.22) and +(0,0.45) .. ++(0.02,-1.25)             
    .. controls +(0,-0.1) and +(0,0.2) .. ++(0.16,-0.3)             
    -- ++(0,-7.25) -- ++(0.1,-0.1) ++ (-0.6,0)             
    -- ++(0.1,0.1) -- ++(0,0.8) -- ++(-1,0);

\node[ode,pin={[align=center,pin edge={thick}]left:Anode\\\( + \)}] at (-1.2,0) (anode) {};         
\node[ode,pin={[align=center,pin edge={thick}]right:Cathode\\\( - \)}] at (1.2,0) (cathode) {};

\coordinate[pin={[pin edge={thick}]left:Oxygen}] (ox) at (-1.2,4.7);         
\coordinate[pin={[pin edge={thick}]right:Hydrogen}] (hy) at (1.2,5.1);         
\coordinate[pin={[pin distance=2.5cm,align=center,pin edge={thick}]right:Acidulated\\water}] (aw) at (0.2,8.6);

\node[cork] at (-1.2,-0.9) {};         
\node[cork] at (1.2,-0.9) {};

\begin{scope}[shift={(1.2,6.8)},fill=white]             
    \filldraw (0.45,-0.05) rectangle (0,0.05);             
    \filldraw[fill=white,rounded corners=1pt] (-0.3,-0.15) rectangle ++(0.6,0.3);             
    \filldraw[fill=white] (0.45,0) circle (0.075 and 0.2);             
    \filldraw[fill=white] (0,0) circle (0.075);         
\end{scope}         
\begin{scope}[xscale=-1,shift={(1.2,6.8)},fill=white]             
    \filldraw (0.45,-0.05) rectangle (0,0.05);             
    \filldraw[fill=white,rounded corners=1pt] (-0.3,-0.15) rectangle ++(0.6,0.3);             
    \filldraw[fill=white] (0.45,0) circle (0.075 and 0.2);             
    \filldraw[fill=white] (0,0) circle (0.075);         
\end{scope}

\node (bat) at (-0.5,-3) [battery];         
\node (amp) at (1,-3) [amperemeter];         
\node (res) at (3,-3) [draw,minimum width=15mm,minimum height=2.5mm]{};
\draw (anode) |- (bat);         
\draw (bat) -- (amp);         
\draw (amp) -- (res);         
\draw[->] (cathode) -- (cathode|-0,-1.5) -| (res.40);

\node (oxlabel) at (-5,4) {Reaction at Anode};
\node (oxygenreacc) at (-5,3.5) {$\ce{3H2O -> \frac{1}{2}O2 +2H3O+ +2e-}$};
\node (hydlable) at (5,4) {Reaction at Cathode};
\node (hydrogenreacc) at (5,3.5) {$\ce{2H3O+ +2e- ->H2 +2H2O}$};
\node (overallreacclabel) at (-5,-1) {Overall Reaction};
\node (overallreacc) at (-5,-1.5) {$\ce{H2O ->\frac{1}{2}O2 + H2}$};
\end{tikzpicture}

enter image description here

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