A novel catalyst free carbon nanotube (CNT) electrode was fabricated by a Carbo Thermo Carbide Conversion (CTCC) method. The morphology and nanostructure of the CNT electrodes were characterized by transmission electron microscopy (TEM) and Raman spectroscopy. Electrochemical characterization using potassium ferricyanide, ferroin and catechol shows these CNTs have higher current capacity, faster electron transfer rate and larger microscopic surface area than glassy carbon (GC) electrode.

The electrocatalytic reduction of CO 2 by cis-H,T-[Rh 2 (mhp) 2 (L) 2 ][BF 4 ] 2 , where mhp − = the deprotonated 6-methyl-2-hydroxypyridine anion and L = 1,10phenanthroline (phen; Rh 2 -phen) and dipyrido[3,2-f:2′,3′h]quinoxaline (dpq; Rh 2 -dpq 2 ), was investigated. The cis-H,T-[Rh 2 (mhp) 2 (L) 2 ] 2+ architecture is composed of two electron-rich mhp − bridging ligands, two electron-accepting diimine chelating ligands, L, and the redox-active Rh 2 (II,II) bimetallic core. Rh 2 -phen 2 and Rh 2 -dpq 2 display metalcentered Rh 2 II,II/II,I reduction waves at −0.36 and −0.29 V vs Ag/AgCl, followed by a reduction event localized on the phen and dpq ligands at −1.15 V and −1.07 vs Ag/AgCl, respectively, in CH 3 CN under N 2 . A second metal-centered reduction is observed at −1.70 and −1.52 V vs Ag/AgCl in Rh 2 -phen 2 and Rh 2 -dpq 2 , respectively. Under a CO 2 atmosphere and 3 M H 2 O as the proton source, both complexes display catalytic currents near the third reduction couple. Although both Rh 2 -phen 2 and Rh 2 -dpq 2 possess comparable electronic structures and steric environments, they exhibit surprisingly different selectivity and efficiency in bulk electrolysis experiments. Rh 2 -phen 2 is both more selective and efficient for the reduction of CO 2 to HCOOH than H + to H 2 than Rh 2 -dpq 2 . The difference in catalytic activity between the two complexes is attributed to the greater electron density closer to the dirhodium core upon reduction of the diimine ligand in Rh 2 -phen 2 as compared to Rh 2 -dpq 2 . In Rh 2 -dpq 2 , the dpq-based reduction is expected to be mainly localized at the distal pyrazine unit and to exert a less pronounced effect on subsequent reactivity taking place at the dirhodium core. In addition, the reduction of the dpq ligand in Rh 2 -dpq 2 is followed by protonation of the nitrogen atoms on the pyrazine unit, thus reducing its ability to store and then supply a redox equivalent required for catalysis at the dirhodium core. The present work provides structural and electronic guidelines for the design of selective and efficient bimetallic catalysts.

Structural tuning of dirhodium electrocatalysts for the selective reduction of CO2 to HCOOH.