  Catalytic engines can use hydrogen peroxide as a chemical fuel in order to
drive motion at the microscale. The chemo-mechanical actuation is a complex
mechanism based on the interrelation between catalytic reactions and
electro-hydrodynamics phenomena. We studied catalytic micropumps using
fluorescence confocal microscopy to image the concentration of protons in the
liquid. In addition, we measured the motion of particles with different charges
in order to map the spatial distributions of the electric field, the
electrostatic potential and the fluid flow. The combination of these two
techniques allows us to contrast the gradient of the concentration of protons
against the spatial variation in the electric field. We present numerical
simulations that reproduce the experimental results. Our work sheds light on
the interrelation between the different processes at work in the
chemo-mechanical actuation of catalytic pumps. Our experimental approach could
be used to study other electrochemical systems with heterogeneous electrodes.
