Chemical surface tuning electrocatalysis of redox-active nanoparticles

This work focuses on electron transfer (ET) and electrocatalysis of inorganic hybrid Prussian blue nanoparticles (PBNPs, 6 nm) immobilized on different chemical surfaces. Through surface self-assembly chemistry, we have enabled to tune chemical properties of the electrode surface. Stable immobilization of the PBNPs on Au(111) surfaces modified by self-assembled monolayers (SAMs) with various terminal groups including positively charged groups (–NH₃+), negatively charged groups (-COO^-), and neutral and hydrophobic groups (-CH₃) has been achieved. The surface microscopic structures of immobilized PBNPs are characterized by atomic force microscopy (AFM). Reversible electron transfer (ET) was detected by cyclic voltammetry (CV) of the PBNPs on all the surfaces. ET kinetics can be controlled by adjusting the chain length of the SAMs. The rate constants are found to depend exponentially on the ET distance, with a decay factor (β) of ca. 0.9, 1.1, 1.3 per CH₂, respectively. This feature suggests a tunneling mechanism adopted by the nanoparticles, resembling that for metalloproteins in a similar assembly. High-efficient electrocatalysis towards the reduction of H₂O₂ is observed, and possible catalytic mechanisms are discussed.