Surface Generation of a Cobalt‐Derived Water Oxidation Electrocatalyst Developed in a Neutral HCO₃⁻/CO₂ System

Abstract

near-neutral pH (pH = 6.7-6.8), the cobalt-bicarbonate-derived electrocatalyst (Co-Ci) is readily generated on conducting oxide electrode surfaces such as FTO (fl uorine-doped tin oxide) and ITO (indium tin oxide), or on a glassy carbon (GC) anode and show remarkable activity for water oxidation during extended period operation (Figure 1 ). At 1.37 V (vs NHE) in a HCO 3 − / CO 2 system at near-neutral pH, a stable oxygen evolution current density ( J ) of ≈2.0 mA cm −2 was obtained during constantpotential electrolysis (CPE) of water. The anodic current was sustained for many hours of electrochemical operation with no noticeable decrease in the performance. We also show that under neutral pH conditions, bicarbonate is an excellent electrolyte system that provides more stability to the electrodeposited Co-oxide derived water oxidation catalyst in comparison with the neutral phosphate buffer. As the Co-Ci is assembled in a CO 2 enriched environment, the catalytic system can operate along with a carbon dioxide reduction module in the same electrochemical setup to make liquid fuel products (such as formic acid or methanol). The catalytic system also shows remarkable activity in a clean bicarbonate electrolyte (no CO 2 bubbling) without having Co 2+ in the solution. Energy-dispersive X-ray (EDX) spectroscopy shows the presence of carbon (about 30%)

Carbonate-coordinated cobalt co-catalyzed BiVO4/WO3 composite photoanode tailored for CO2 reduction to fuels

“…The BiVO 4 /WO 3 shows predominant M-O peak at 529.3 eV with a very small peak at 531 eV (Figures S5b and 2c). The trend is reversed in Co-Ci/ BiVO 4 /WO 3 (Figures S6b and 2d), which showed a small M-O peak and a large non-metal oxide peak at 531 eV [25,30]. Surface elemental composition by XPS in Table S1 showed increase in C, decrease in O, and a large decrease in Bi and V after Co-Ci deposition.…”

“…BiVO 4 /WO 3 predominantly showed C-C peak from contaminated carbon with a small peak at 284.6.0 eV ( Figure S5). However, increase in intensity of C 1s peak and stronger 288.0 eV peak upon Co-Ci deposition indicate the presence of a CO 3 2 À -like species (Figures 2b,c and S5) [25,30]. More obvious indication of the carbonate species in Co-Ci/BiVO 4 / WO 3 could be observed from the O 1s spectrum, which gave peaks at 529.3 eV assigned to M-O and at 531 eV assigned to -CO x and surface -O-H groups.…”

“…Carbon C 1s showed two peaks at 284.6 eV (assigned for C-C) and 288.0 eV (assigned to -C(O)O-and -C-OH) [25,30]. BiVO 4 /WO 3 predominantly showed C-C peak from contaminated carbon with a small peak at 284.6.0 eV ( Figure S5).…”

Recent Advances in the BiVO4 Photocatalyst for Sun-Driven Water Oxidation: Top-Performing Photoanodes and Scale-Up Challenges

“…Joya et al [53] reported the use of a cobalt carbonate (Co-Ci) OEC produced in situ, generated from a CO 2 saturated bicarbonate solution containing Co 2+ ions. They reported that the Co-Ci OEC in a HCO 3 − /CO 2 electrolyte showed a stable current density of >2 mA/cm 2 at 1.35 V vs. NHE (normal hydrogen electrode), and remained active for 16 h. It was also reported that Co-based OECs, such as Co-Pi and Co-Ci, tend to lose stability in a phosphate electrolyte system during anodic water oxidation, although, they also exhibit a sustained current density and higher stability in a HCO 3 − /CO 2 system.…”

Efficient electrochemical water oxidation in neutral and near-neutral systems with a nanoscale silver-oxide catalyst

“…This oxygen evolution onset potential and catalytic current density of the silver-oxide based electrocatalyst are comparable to those observed for Ni-oxide and Co-oxide based materials generated electrochemically in near-neutral conditions. [17,27] RuO 2 and IrO 2 are the benchmark materials for water oxidation in acidic condition. The catalytic activity data for AgOx-NP and RuO 2 and IrO 2 in near-neutral borate buffer show that the AgOx-NP sample have comparable oxygen on set and water oxidation activity ( Figure S1).…”