Photo-Electrochemical Oxygen Evolution Reaction by Biomimetic CaMn2O4 Catalyst

Abstract

Calcium manganese oxide catalysts are a new class of redox catalysts with significant importance because of their structural similarity to natural oxygen-evolving complex in plant cells and the earth-abundant elemental constituents. In the present study, the photo-electrocatalytic properties of CaMn2O4 in water-splitting were investigated. CaMn2O4 powders with irregular shapes and nanowire shapes were synthesised using mechanochemical processing and a hydrothermal method, respectively. The anode in a photo-electrochemical cell was fabricated by embedding CaMn2O4 powders within polypyrrole. The results showed that CaMn2O4 induced a higher dark and light current in comparison to the control sample (polypyrrole alone). CaMn2O4 nanowires exhibited higher dark and light current in comparison to irregular-shaped CaMn2O4 powders. The difference was attributable to the higher surface area of nanowires compared to the irregular-shaped particles, rather than the difference in exposed crystal facets.

Mechanochemical synthesis of metal oxide nanoparticles

“…After heat treatment of the as-milled powder at 600 °C for 1 h, Ca 2 Mn 3 O 8 nanoparticles had diameters in the range of 30–100 nm. CaMn 2 O 4 and CaMnO 3 nanoparticles were obtained in a similar manner, but using K 2 SO 4 by-product phase instead of KCl 90 . This is because K 2 SO 4 has a higher melting point (1069 °C) than KCl (770 °C) and the thermal decomposition of CaMn 2 (CO 3 ) 3 and CaMn(CO 3 ) 2 required heat treatment at higher than 770 °C.…”

“… Material Average size (nm) Chemical reactions Ref. BaFe 12 O 19 20–100 nm 1.2BaCl 2 + 12FeCl 3 + 38.4NaOH → BaFe 12 O 19 + 38NaCl + 19H 2 O 95 ZnWO 4 20–50 nm H 2 WO 4 + ZnCl 2 + Na 2 CO 3 + 4NaCl → ZnWO 4 + 6NaCl + H 2 O + CO 2 111 Ca 2 Mn 3 O 8 10–20 nm 2CaCl 2 + 3MnCl 2 + 5K 2 CO 3 + 29KCl → Ca 2 Mn 3 (CO 3 ) 5 + 39KCl; Ca 2 Mn 3 (CO 3 ) 5 + 1.5O 2 → Ca 2 Mn 3 O 8 + 5CO 2 89 CaMn 2 O 4 200nm-2μm CaSO 4 + 2MnSO 4 + 3K 2 CO 3 + 11K 2 SO 4 → CaMn 2 (CO 3 ) 3 + 14K 2 SO 4 ;CaMn 2 (CO 3 ) 3 + 0.5O 2 → CaMn 2 O 4 + 3CO 2 90 CaMnO 3 50–200 nm CaSO 4 + MnSO 4 + 2K 2 CO 3 + 7K 2 SO 4 → CaMn(CO 3 ) 2 + 9K 2 SO 4 ; CaMn(CO 3 ) 2 + 0.5O 2 → CaMnO 3 + 2CO 2 90 CoFe 2 O 4 5–100 nm CoCl 2 + 2FeCl 3 + 8NaOH → CoFe 2 O 4 + 8NaCl 112 LaCoO 3 <100 nm LaCl 3 ...…”

Conducting-Polymer Nanocomposites as Synergistic Supports That Accelerate Electro-Catalysis: PEDOT/Nano Co3O4/rGO as a Photo Catalyst of Oxygen Production from Water

“…As such, it is important to develop techniques that maximize the performance of nano-particulate electro-catalysts, which are typically deposited as thin films on electrode surfaces. One approach that has recently been developed by our research group in this respect involves the use of conducting polymers [2] and conductive additives as supports that create synergies with the electro-catalyst to maximally accelerate the overall electrocatalytic rate [3][4][5][6][7][8][9][10].…”

“…In effect, the photo-(or)electro-catalyst is deposited in a thin film nanocomposite that contains within it very specific proportions of a uniformly dispersed conducting polymer and conductive additive. The conducting polymer provides a large number of electrical connections to the innumerable catalytic sites on the many surfaces of the catalyst nanoparticles, along the shortest possible connection pathways to the electrode, while the conductive additive decreases the resistance of those pathways and increases visible light absorbance [3][4][5][6][7][8][9][10].…”

“…This is necessary to ensure that the largest possible quantity of catalyst nanoparticles is present, yielding the highest possible catalytic activity. In this way, the competing requirements of maximum catalytic loading, and the best electrical connection to each catalytic site, along the shortest and most conductive pathway to the electrode, are simultaneously achieved [3][4][5][6][7][8][9][10].…”