How can I increase the current on a voltaic cell for high school lab?
Increase the area of the electrodes (e.g more ribbon).
Decrease the resistance of the electrolyte (e.g. reduce the spacing between electrodes, increase concentration of salts).
Reduce polarization of electrodes (bubbles on surface, etc.). Scrape or lightly sandpaper the electrodes and test immediately after immersion, before bubbles form.