Julian A. Vigil

Electrodeposited MnOx/PEDOT Composite Thin Films for the Oxygen Reduction Reaction

Manganese oxide (MnOx) was anodically coelectrodeposited with poly(3,4-ethylenedioxythiophene) (PEDOT) from an aqueous solution of Mn(OAc)2, 3,4-ethylenedioxythiophene, LiClO4 and sodium dodecyl sulfate to yield a MnOx/PEDOT composite thin film. The MnOx/PEDOT film showed significant improvement over the MnOx only and PEDOT only films for the oxygen reduction reaction, with a >0.2 V decrease in onset and half-wave overpotential and >1.5 times increase in current density. Furthermore, the MnOx/PEDOT films were competitive with commercial benchmark 20% Pt/C, outperforming it in the half-wave ORR region and exhibiting better electrocatalytic selectivity for the oxygen reduction reaction upon methanol exposure. The high activity of the MnOx/PEDOT composite is attributed to synergistic charge transfer capabilities, attained by coelectrodepositing MnOx with a conductive polymer while simultaneously achieving intimate substrate contact.

Cobalt phosphide-based nanoparticles as bifunctional electrocatalysts for alkaline water splitting

Cobalt phosphide-based nanoparticles serve as effective bifunctional electrocatalysts for alkaline water splitting reactions with activities comparable to more expensive precious metal catalysts.

Nanostructured cobalt phosphide-based films as bifunctional electrocatalysts for overall water splitting

Nanostructured cobalt phosphide-based films were prepared using a simple, three-step electrodeposition–thermal annealing–phosphidation method. The films are effective electrocatalysts for the hydrogen evolution reaction in acidic and alkaline electrolytes, and the oxygen evolution reaction in alkaline electrolyte. A symmetrical alkaline electrolysis cell with low overpotential of 0.41–0.51 V was demonstrated.

Nanoscale Carbon Modified α-MnO2 Nanowires: Highly Active and Stable Oxygen Reduction Electrocatalysts with Low Carbon Content

Carbon-coated α-MnO2 nanowires (C-MnO2 NWs) were prepared from α-MnO2 NWs by a two-step sucrose coating and pyrolysis method. This method resulted in the formation of a thin, porous, low mass-percentage amorphous carbon coating (<5 nm, ≤1.2 wt % C) on the nanowire with an increase in single-nanowire electronic conductivity of roughly 5 orders of magnitude (α-MnO2, 3.2 × 10-6 S cm-1; C-MnO2, 0.52 S cm-1) and an increase in surface Mn3+ (average oxidation state: α-MnO2, 3.88; C-MnO2, 3.66) while suppressing a phase change to Mn3O4 at high temperature. The enhanced physical and electronic properties of the C-MnO2 NWs-enriched surface Mn3+ and high conductivity-are manifested in the electrocatalytic activity toward the oxygen reduction reaction (ORR), where a 13-fold increase in specific activity (α-MnO2, 0.13 A m-2; C-MnO2, 1.70 A m-2) and 6-fold decrease in charge transfer resistance (α-MnO2, 6.2 kΩ; C-MnO2, 0.9 kΩ) were observed relative to the precursor α-MnO2 NWs. The C-MnO2 NWs, composed of ∼99 wt % MnO2 and ∼1 wt % carbon coating, also demonstrated an ORR onset potential within 20 mV of commercial 20% Pt/C and a chronoamperometric current/stability equal to or greater than 20% Pt/C at high overpotential (0.4 V vs RHE) and high temperature (60 °C) with no additional conductive carbon.

Hybrid PEDOT/MnOx nanostructured electrocatalysts for oxygen reduction

A series of hybrid poly(3,4-ethylenedioxythiophene)/manganese oxide (PEDOT/MnOx) thin films have been prepared via a stepwise approach: electrodeposition of PEDOT, followed by formation of MnOx particles by a spontaneous redox reaction between PEDOT and KMnO4. Electrocatalytic characterization of the PEDOT/MnOx thin films demonstrates high activity toward the oxygen reduction reaction (ORR), with a shift in intrinsic ORR onset and half-wave potentials by ca. 0.2 V to lower overpotential relative to the PEDOT thin film. The most active PEDOT/MnOx thin film electrocatalyst, P-MnOx-20, demonstrates superior activity relative to the commercial 20% Pt/C catalyst in the half-wave region of the ORR potential window at equal mass loading, with a half-wave potential of 0.83 V (20% Pt/C, 0.81 V) and charge transfer resistance of 479 Ω (20% Pt/C, 862 Ω). The P-MnOx-20 film also demonstrates preference to a pseudo-four electron ORR pathway (n = 3.8) and high specific ORR activity, when considered on both a total mass (−96 mA mgtotal−1; 20% Pt/C: −108 mA mgtotal−1) and metal (or metal oxide) mass basis (−296 mA mgMnOx−1; 20% Pt/C: −540 mA mgPt−1). The P-MnOx-20 film has been identified as the most active PEDOT/ceramic composite electrocatalyst reported to date, which is rationalized by the high surface concentration of Mn(III), strong electronic coupling between PEDOT and MnOx, as well as a high active site density and efficiency achieved by the stepwise electrodeposition-redox approach.

Insights into the spontaneous formation of hybrid PdOx/PEDOT films: electroless deposition and oxygen reduction activity

Hybrid palladium oxide/poly(3,4-ethylenedioxythiophene) (PdOx/PEDOT) films were prepared through a spontaneous reaction between aqueous PdCl42− ions and a nanostructured film of electropolymerized PEDOT. Spectroscopic and electrochemical characterization indicate the presence of mixed-valence Pd species as-deposited (19 ± 7 at% Pd0, 64 ± 3 at% Pd2+, and 18 ± 4 at% Pd4+ by X-ray photoelectron spectroscopy) and the formation of stable, electrochemically reversible Pd0/α-PdOx active species in alkaline electrolyte and furthermore in the presence of oxygen. The elucidation of the Pd speciation as-deposited and in solution provides insight into the mechanism of electroless deposition in neutral aqueous conditions and the electrocatalytically active species during oxygen reduction in alkaline electrolyte. The PdOx/PEDOT film catalyses 4e− oxygen reduction (n = 3.97) in alkaline electrolyte at low overpotential (0.98 V vs. RHE, onset potential), with mass- and surface area-based specific activities competitive with, or superior to, commercial 20% Pt/C and state-of-the-art Pd- and PEDOT-based nanostructured catalysts. The high activity of the nanostructured hybrid PdOx/PEDOT film is attributed to effective dispersion of accessible, stable Pd active sites in the PEDOT matrix.