The physical properties, including morphology, thickness, porosity, crystalline structure, and surf ace/bulk compositions, of the as-prepared CuxSny (x = at. % Cu, y = at.% Sn) and CuxInz (z = at.% In) bimetallic catalysts were f irst evaluated using different material characterization techniques. As shown in Figure and Figure , porous Cu-Sn and Cu-In bimetallic f oams with a range of compositions (various In and Sn contents) were successfully synthesized through a one-step co-electrodeposition synthesis approach, as described in experimental section in SI. While the resulting materials exhibited similar dendrite-like microstructures, the f ine microstructure of these dendrites showed some variation dependent on the Cu/In and Cu/Sn molar ratios in the deposition solution (see Figure ). The shape of these electrodeposited dendrites is mainly controlled by the rate of metal deposition and the rate of the concurrent hydrogen evolution reaction. The presence of either In or Sn in the Cu deposition bath is seen to have a significant impact on the nucleation, growth and break-off rates of the in-situ generated hydrogen bubbles, and hence on the f ine structure and physical properties (e.g., porosity, thickness, etc) of the obtained porous foams . The presence of Cu as foaming agent is essential to create these dendritic microstructures (porous f oams), since the f abricated pure Sn and In did not show any dendrite-like structures. Contrary to the mixed metal depositions, electrodeposition from solutions of only Sn resulted in porous Sn thin f ilms composed of interconnected Sn tubes (f ishbone-like structures, Figure ), while pure In exhibited a rough thin layer composed of In grains (Figure ).