Liquid cell scanning transmission electron microscopy characterization of combined chemical and electrochemical reduction of palladium

We systematically investigate the effect of the driving force on the growth of palladium nanoparticles by comparing electrochemical reduction of polyvinylpyrollidone-stabilized palladium nitrate solution with chemical reduction by ascorbic acid using in-situ liquid cell transmission electron microscopy. Electrochemical data is simultaneously collected while high spatial resolution is maintained. As a chemical reductant, ascorbic acid results in the formation of smaller, more tightly spaced palladium nanoparticles through increased nucleation. When present during electrochemical reduction of palladium, ascorbic acid reduces the degree to which dendrites form due to the growth of a more compact palladium layer. Because the nanoparticles formed during chemical reduction have diameters on the order of a nanometer and are invisible under full liquid conditions, we employ electrochemical water splitting to generate a gas bubble in order to observe the process in real time. This is a step towards real-time characterization of complex solution-phase growth in which multiple pathways exist for metals to reduce and combinations of additives interact to control size and shape.