Voltammetry of Lanthanide Triflate Complexes in Acetonitrile: Catalysis for Single Carbon C1 Species

Nadeesha P.W. Rathuwadu; Johna Leddy

doi:10.1149/MA2025-02612854mtgabs

Lanthanides and lanthanide complexes are largely unexplored as electrocatalysts. Across the period, the lanthanides LNs are broadly chemically and physically similar. However, variation in the number of available 4f electrons may refine optimization of electrocatalyst.[1-3] Here, impacts of ytterbium trflate Yb(OTf) 3 electrocatalyst are surveyed across single carbon C1 species of methanol, formaldehyde, formic acid, carbon monoxide, and carbon dioxide.[4] Triflate ligand OTf - is trifluorosulfonate CF3SO 3 - , the anion of triflic acid. Thermodynamically, C1 species are easily electrolyzed, but C1 mechanisms depend on electrons and protons and the kinetics are slow. Cyclic voltammograms at 50 mV/s in acetonitrile with 0.10 M TBABF 4 and a C1 analyte are undertaken at a 0.45 cm 2 platinum electrode that is either unmodified or modified with a Nafion film. The electrocatalyst 1.0 mM Yb(OTf) 3 may be added to the electrolyte. In all cases compared to Nafion film electrodes, currents were smallest at unmodified platinum. For Nafion films, currents and charge were larger with Yb(OTf) 3 in solution. The magnitude of current enhancement at Nafion films with Yb(OTf) 3 as compared to Nafion with no lanthanide complex vary with C1 species. In all cases, the potential was first swept to negative potentials, reversed at the cathodic solvent limit, and then swept to positive potentials to the anodic solvent limit. The potential range was about 4 V. Potentials are reported versus a silver quasireference electrode (QRE). CH 3 OH : Oxidation currents for 10 % CH 3 OH are enhanced by 3x at -0.5 V with Yb(OTf) 3 . Current at 1.6 V, ~ 1 mA/cm 2 with Yb(OTf) 3 but negligible with no Yb(OTf) 3 . Solvent reduction onsets 0.2 V sooner with Yb(OTf) 3 . HCOH : CVs for 4 % HCOH are complex, with slightly higher currents (<20 %) with Yb(OTf) 3 . HCOOH : Largest enhancements in charge and current are found for 10 % HCOOH. At -0.1 V, current is ~60 % high and charge is ~2x with Yb(OTf) 3 . At 1.6 V, current is ~3.3 x and charge is > 10 x. CO : Purged with 1:1 CO:H2, CVs are complex. There is evidence of adsorption ~0.4 V, with stripping waves without Yb(OTf) 3 , and broader waves and more charge (~2x) on the reverse (oxidative) sweep with Yb(OTf) 3 . CO 2 : CO 2 was evaluated at unmodified Pt, with each Nd(OTf) 3 , Gd(OTf) 3 , and Yb(OTf) 3 in solution. Electrolyte was purged with either N 2 or CO 2 . With CO 2 , hydrogen evolution at -2 V and the return oxidation wave for LN(OTf) 3 at -0.2 V are suppressed. Of the three LN(OTf) 3 complexes, kinetics for Yb(OTf) 3 are slowed. In summary, Yb(OTf) 3 at Nafion modified Pt catalyzes oxidation of methanol and formic acid substantially, but impacts of Yb(OTf) 3 on aldehyde and CO are more complex and less apparent. For CO 2 , choice of lanthanide may impact catalysis.

Voltammetry of Lanthanide Triflate Complexes in Acetonitrile: Catalysis for Single Carbon C1 Species

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