Robust Sub‐Monolayers of Co₃O₄ Nano‐Islands: A Highly Transparent Morphology for Efficient Water Oxidation Catalysis

Abstract

The scalable synthesis of highly transparent and robust sub‐monolayers of Co3O4 nano‐islands, which efficiently catalyze water oxidation, is reported. Rapid aerosol deposition of Co3O4 nanoparticles and thermally induced self‐organization lead to an ultra‐fine nano‐island morphology with more than 94% light transmission at a wavelength of 500 nm. These transparent sub‐monolayers demonstrate a remarkable mass‐weighted water oxidation activity of 2070–2350 A gCo3O4−1 and per‐metal turnover frequency of 0.38–0.62 s−1 at an overpotential of 400 mV in 1 m NaOH aqueous solution. This mixed valent cobalt oxide structure exhibits excellent long‐term electrochemical and mechanical stability preserving the initial catalytic activity over more than 12 h of constant current electrolysis and 1000 consecutive voltammetric cycles. The potential of the Co3O4 nano‐islands for photoelectrochemical water splitting has been demonstrated by incorporation of co‐catalysts in GaN nanowire photoanodes. The Co3O4‐GaN photoanodes reveal significantly reduced onset overpotentials, improved photoresponse and photostability compared to the bare GaN ones. These findings provide a highly performing catalyst structure and a scalable synthesis method for the engineering of efficient photoanodes for integrated solar water‐splitting cells.

Modulating Activity through Defect Engineering of Tin Oxides for Electrochemical CO2 Reduction

“…[26,28] In this work, the FSP-SnO 2 catalysts were synthesized at a feedrate of 3, 5, and 7 mL min −1 and are denoted as FSP-SnO 2 -3, FSP-SnO 2 -5, and FSP-SnO 2 -7, respectively (detailed in the Experimental Section). By varying the precursor feed rate to the flame, the flame conditions can be controlled and thus allow for the tuning of material properties such as particle size and morphology, crystallinity, and defects.…”

High‐Temperature One‐Step Synthesis of Efficient Nanostructured Bismuth Vanadate Photoanodes for Water Oxidation

“…Figure a shows a schematic for the high‐temperature fabrication of the BiVO 4 photoanodes. A flame synthesis setup previously described in detail for the fabrication of ultrafine Co 3 O 4 nano‐islands was used . Here, atomization and combustion of the liquid precursor solution, followed by rapid quenching by the entrained air, results in the nucleation of BiVO 4 clusters of few nanometers, and the latter grow in the gas phase by condensation and Brownian's coagulation.…”

Research advances towards large-scale solar hydrogen production from water

“…248,[302][303][304][305][306] Flame spray pyrolysis as an aerosol deposition method is also highly scalable for facile and fast fabrication of various nanostructured (photo)electrodes. [307][308][309][310] A production rate of a few kilograms per hour is achievable using lab-scale burners with tunable specific surface area and catalytic activity of the produced nanomaterials. [311][312] Notably, although the electrocatalysts produced by these industrially viable fabrication techniques demonstrated excellent catalytic activities, 310,313 the photoelectrodes fabricated using them still showed poorer photoactivities than those state-of-the-art photoelectrodes using conventional lab-scale fabrication techniques.…”

“…[307][308][309][310] A production rate of a few kilograms per hour is achievable using lab-scale burners with tunable specific surface area and catalytic activity of the produced nanomaterials. [311][312] Notably, although the electrocatalysts produced by these industrially viable fabrication techniques demonstrated excellent catalytic activities, 310,313 the photoelectrodes fabricated using them still showed poorer photoactivities than those state-of-the-art photoelectrodes using conventional lab-scale fabrication techniques. 254 reported that large size led to a significant potential drop for the same photoelectrode (Figure 39a, b).…”