Shape-controlled electrodeposition of standing Rh nanoplates on indium tin oxide substrates and their electrocatalytic activity toward formic acid oxidation

Standing rhodium nanoplates were successfully synthesized on indium tin oxide (ITO) substrate by electrochemical deposition using RhCl ₃ and sodium citrate as precursor and capping agent, respectively. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed that most of the Rh nanoplates are perpendicularly orientated to the ITO substrate with an average length of 140 nm, an average height of 120 nm, and a thickness of 25 nm. X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicated that the standing Rh nanoplates (s-RhNPs) were single crystals with face-centered cube pattern. The factors influencing the electrochemical growth of Rh nanocrystals (RhNCs) were systematically studied. It was found that the transient nucleation step at a high overpotential before electrochemical growth is crucial to the formation of a uniform s-RhNPs array. The morphology of RhNCs is very sensitive to the applied growth potential and s-RhNPs can only be obtained in a narrow potential range of -0.240 to -0.260 V. Moreover, the concentrations of both the precursor (RhCl ₃) and the capping agent (sodium citrate) have significant effect on the morphology of RhNCs. A mechanism was proposed to explain the electrochemical growth and orientation of s-RhNPs. Electrocatalyic measurements demonstrated that the as-synthesized s-RhNPs, compared with isotropic RhNCs, exhibit higher catalytic current density for formic acid electrooxidation.