Au-based/electrochemically etched cavity-microelectrodes as optimal tool for quantitative analyses on finely dispersed electrode materials: Pt/C, IrO2-SnO2 and Ag catalysts

Evaluating Fe-Site and Vacancy Dependent Intrinsic Activity of NiFe Layered Double Hydroxides through Cavity Microelectrodes

We report evaluating the intrinsic activity of Ni(OH)₂, NiFe layered double hydroxides (LDHs), and NiFe-LDH having vacancies for oxygen evolution reaction (OER) by the use of cavity microelectrodes (CMEs) with controllable mass loading. The number of active Ni sites (N_Ni-sites) ranging from 1 × 10¹² to 6 × 10¹² is quantitatively correlated with OER current, which reveals that the introduction of Fe-sites and vacancies increases the turnover frequency (TOF) from 0.027 to 0.118 and 0.165 s^-1, respectively. Electrochemical surface area (ECSA) is further quantitatively correlated with N_Ni-sites, which indicates that N_Ni-sites per unit ECSA (N_Ni-per-ECSA) is decreased by the introduction of Fe-sites and vacancies. Therefore, the difference of OER current per unit ECSA (J_ECSA) is reduced compared with that of TOF. The results demonstrate that CMEs provide a good platform to evaluate intrinsic activity with TOF, N_Ni-per-ECSA, and J_ECSA more reasonably.

ORR in Non-Aqueous Solvent for Li-Air Batteries: The Influence of Doped MnO2-Nanoelectrocatalyst

One of the major drawbacks in Lithium-air batteries is the sluggish kinetics of the oxygen reduction reaction (ORR). In this context, better performances can be achieved by adopting a suitable electrocatalyst, such as MnO2. Herein, we tried to design nano-MnO2 tuning the final ORR electroactivity by tailoring the doping agent (Co or Fe) and its content (2% or 5% molar ratios). Staircase-linear sweep voltammetries (S-LSV) were performed to investigate the nanopowders electrocatalytic behavior in organic solvent (propylene carbonate, PC and 0.15 M LiNO3 as electrolyte). Two percent Co-doped MnO2 revealed to be the best-performing sample in terms of ORR onset shift (of ~130 mV with respect to bare glassy carbon electrode), due to its great lattice defectivity and presence of the highly electroactive γ polymorph (by X-ray diffraction analyses, XRPD and infrared spectroscopy, FTIR). 5% Co together with 2% Fe could also be promising, since they exhibited fewer diffusive limitations, mainly due to their peculiar pore distribution (by Brunauer-Emmett-Teller, BET) that disfavored the cathode clogging. Particularly, a too-high Fe content led to iron segregation (by energy dispersive X-ray spectroscopy, EDX, X-ray photoelectron spectroscopy, XPS and FTIR) provoking a decrease of the electroactive sites, with negative consequences for the ORR.

Redox titration of gold and platinum surface oxides at porous microelectrodes

Cavity-microelectrodes were used to investigate surface oxides on supported platinum nanoparticles and nanoporous gold with the surface interrogation mode of scanning electrochemical microscopy.

The Influence of Carbonaceous Matrices and Electrocatalytic MnO₂ Nanopowders on Lithium-Air Battery Performances

Here, we report new gas diffusion electrodes (GDEs) prepared by mixing two different pore size carbonaceous matrices and pure and silver-doped manganese dioxide nanopowders, used as electrode supports and electrocatalytic materials, respectively. MnO₂ nanoparticles are finely characterized in terms of structural (X-ray powder diffraction (XRPD), energy dispersive X-ray (EDX)), morphological (SEM, high-angle annular dark field (HAADF)-scanning transmission electron microscopy (STEM)/TEM), surface (Brunauer Emmet Teller (BET)-Barrett Joyner Halenda (BJH) method) and electrochemical properties. Two mesoporous carbons, showing diverse surface areas and pore volume distributions, have been employed. The GDE performances are evaluated by chronopotentiometric measurements to highlight the effects induced by the adopted materials. The best combination, hollow core mesoporous shell carbon (HCMSC) with 1.0% Ag-doped hydrothermal MnO₂ (M_hydro_1.0%Ag) allows reaching very high specific capacity close to  1400 mAh·g⁻¹. Considerably high charge retention through cycles is also observed, due to the presence of silver as a dopant for the electrocatalytic MnO₂ nanoparticles.