help with subplot tikzpicture please

Question

I want to plot these two stacked bar plots as a subplot in one figure next to each other here is the code and my current output

\begin{figure}[htbp]

\centering

\subfigure[Weight comparison]{\begin{tikzpicture}

\begin{axis}[ylabel= Weight (tonne)
,ymin=0,ybar stacked,bar width=1cm,
y tick label style={/pgf/number format/fixed, 
/pgf/number format/1000 sep = \thinspace % Optional if you want to replace comma as the 1000 separator}, xtick=data,x=3.1cm,enlarge x limits=1,area legend,
symbolic x coords={Hybrid fuel cell , 4-stroke system} , legend style={draw=none, legend columns=-1}, width=3cm, height=9cm, legend pos=north west, font=\small]

\addplot coordinates
{(Hybrid fuel cell,0.375) (4-stroke system,0)};

\addplot coordinates
{(Hybrid fuel cell,8.885) (4-stroke system,0)};


\addplot coordinates
{(Hybrid fuel cell,3.9) (4-stroke system,0)};

\addplot coordinates
{(Hybrid fuel cell,0) (4-stroke system,13.064)};


\legend{FC, battery, Motor, DE}
\end{axis}
\end{tikzpicture}}

\subfigure[Volume comparison]{\begin{tikzpicture}

\begin{axis}[ylabel= Volume ($m^{3}$)
,ymin=0,ybar stacked,bar width=1cm,
y tick label style={/pgf/number format/fixed, 
/pgf/number format/1000 sep = \thinspace % Optional if you want to replace comma as the 1000 separator  }, xtick=data,x=3.1cm,enlarge x limits=1,
area legend, symbolic x coords={Hybrid fuel cell, 4-stroke system} , legend style={draw=none, legend columns=-1}, width=3cm, height=9cm, legend pos=north west, font=\small]

\addplot coordinates
{(Hybrid fuel cell,0.66) (4-stroke system,0)};

\addplot coordinates
{(Hybrid fuel cell,4.44) (4-stroke system,0)};


\addplot coordinates
{(Hybrid fuel cell,11.12) (4-stroke system,0)};

\addplot coordinates
{(Hybrid fuel cell,0) (4-stroke system,28.424)};


\legend{FC, battery, Motor, DE}

\end{axis}

\end{tikzpicture}}

\caption{Weight and volume of hybrid fuel cell system compared to 4-stroke diesel engine system}

\end{figure}