Deciphering the molecular mechanism of substrate-induced assembling of gold nanocube arrays toward accelerated electrocatalytic effect employing heterogeneous diffusion fields confinement

The complex electrocatalytic performance of gold nanocubes (AuNCs) is the focus of the presented paper. The faceted shapes of AuNCs and the individual assembling process at the electrode surfaces define heterogeneous conditions for the purpose of electrocatalytic processes. Topographic and electron imaging demonstrated slightly rounded AuNC (avg. 38 nm) assemblies with sizes up to 1 µm, where the dominating patterns are (111) and (200) crystallographic planes. The AuNCs significantly impact the electrochemical performance of the investigated electrode (ITO, GC, bulk gold) systems driven by surface electrons promoting the catalytic effect. Cyclic voltammetry jointly with scanning electrochemical microscopy (SECM) allowed us to decipher the molecular mechanism of substrate-induced electrostatic assembling of gold nanocube arrays, revealing that the accelerated electrocatalytic effect should be attributed to the confinement of the heterogeneous diffusion fields with tremendous electrochemically active surface area variations. The AuNC drop-casting at ITO, GC, and Au led to various mechanisms of heterogeneous charge transfer, where only in the case of GC, the decoration significantly increased both the electrochemically active surface area (EASA) and ferrocyanide redox kinetics. For ITO and Au substrates, AuNC drop-casting lowers system dimensionality rather than expanding the EASA, where Au-Au self-diffusion was also observed. Interactions between the gold, ITO, and GC surfaces with themselves and with surfactant CTAB and ferrocyanide molecules were investigated by performing density functional theory.