In this work, we report the electrochemical response of a family of Co(II) complexes, [Co^II(L)₃]²⁺ and [Co^II(L’)₂]²⁺ (L = 2,2’-bipyridine, 1,10-phenanthroline, 3,4,7,8-tetramethyl-1,10-phenanthroline, 5,6-dimethyl-1,10-phenanthroline, and 4,7-diphenyl-1,10-phenanthroline; L’ = terpyridine and 4-chloro-terpyridine), in the presence and absence of CO₂ in order to understand the role of the redox potential and molecular structure on the molecular catalysis of CO₂ reduction. The tris chelate complexes exhibited three electron transfer processes [Co^II(L)₃]²⁺ ⇄ [Co^III(L)₃]³⁺ + 1e⁻, [Co^ΙΙ(L)₃]²⁺+1e⁻ ⇄ [Co^Ι(L)₃]⁺, and [Co^Ι(L)₃]⁺ + 2e^- ⇄ [Co^Ι(L)(L⁻)₂]⁻. In the case of complexes with 1,10-phen and 2,2-bipy, the third redox process showed a coupled chemical reaction [Co^Ι(L)(L⁻)₂]⁻ → [Co^Ι(L⁻)₂]⁻ + L. For bis chelate complexes, three electron transfer processes associated with the redox couples [Co^ΙΙ(L)₂]/[Co^III(L)₂]³⁺, [Co^ΙΙ(L)₂]²⁺/[Co^Ι(L)₂]⁺, and [Co^Ι(L)₂]⁺/[Co^Ι(L)(L⁻)] were registered, including a coupled chemical reaction only for the complex containing the ligand 4-chloro-terpyridine. Foot to the wave analysis (FOWA) obtained from cyclic voltammetry experiments allowed us to calculate the catalytic rate constant (k) for the molecular catalysis of CO₂ reduction. The complex [Co(3,4,7,8-tm-1,10-phen)₃]²⁺ presented a high k value; moreover, the complex [Co(4-Cl-terpy)₃]²⁺ did not show catalytic activity, indicating that the more negative redox potential and the absence of the coupled chemical reaction increased the molecular catalysis. Density functional theory (DFT) calculations for compounds and CO₂ were obtained to rationalize the effect of electronic structure on the catalytic rate constant (k) of CO₂ reduction.

This work explores the effect of geometry and the presence of a site available for carbon dioxide coordination in molecular catalysis of CO₂ reduction for cobalt complexes using electrochemical and spectroelectrochemical studies. The octahedral complexes [Co^II(bztpen)Br]PF₆ and [Co^II(bpy)₃](BF₄)₂, along with the trigonal bipyramidal complex [Co^II(TPA)Cl]Cl, were selected for this study (where bztepen = N-benzyl-N,N′,N′-tris-(pyridine-2-ylmethyl)-ethylenediamine), TPA = tris (2-pyridimethyl)-amine, and bpy = 2′-2′- pyridine). DFT calculations were performed to predict the geometries of the complexes and to propose the sites at which electron transfer occurs. Among the studied compounds, [Co^II(bpy)₃(BF₄)₂] exhibited the highest catalytic rate constant for CO₂ reduction (k = 1.22 × 10² M⁻¹·s⁻¹) compared to [Co^II(bztpen)Br]PF₆ (k = 8.93 × 10¹ M⁻¹·s⁻¹). The trigonal bipyramidal complex [Co^II(TPA)Cl]Cl presented the lowest catalytic rate constant for CO₂ reduction (k = 1.47 × 10¹ M⁻¹·s⁻¹). UV-Vis spectroelectrochemical studies and DFT calculations suggested the formation of [Co^I(bztpen)(CO)]⁺ and [Co^I(tpa)(CO)]⁺ species, which are associated with catalyst deactivation and may account for the lower performance of CO₂ reduction.

Cathodic materials significantly influence the performance, durability, and sustainability of primary zinc‐air batteries (ZABs). This study focuses on the rational design of highly active metal‐free composites by tailoring the content of N and S heteroatoms in carbon nanotube‐graphene (CNTG) composites. The oxygen reduction reaction (ORR) tests showed onset potentials (E_o) of 0.88 V (N‐CNT) and 0.89 V (N‐graphene) for individual materials and 0.92 V for the N‐CNTG composite, highlighting the advantage of using a composite materialThe N content varied with dicyandiamide and urea, displaying changes in the surface area and N content (7.09 vs. 5.30 at. %), and in pyridinic and quaternary N species. The N content varied with dicyandiamide and urea, showing changes in the surface area and N content (7.09 vs. 5.30 at. %), and in pyridinic and quaternary N species. The abundance of pyridinic‐N species in N‐CNTG using urea enabled a higher ORR activity (E_o=0.92 V). The S incorporation through thiourea improved the E_o to 0.94 V (Pt/C=1.03 V). And, the combination of urea and thiourea resulted in a highly active and durable N,S‐CNTG material, displaying a E_o of 0.96 V, and an activity loss of 8.7 % (Pt/C=25.4 %) after 2000 cycles. In ZAB mode, this material displayed a voltage of 1.35 V, a power density of 107 mW cm⁻², and a specific capacity of 1060 mA h g⁻¹.