A hematite photoelectrode grown on porous and conductive SnO₂ ceramics for solar-driven water splitting

Photoelectrochemical water splitting using solar energy is a highly promising technology to produce hydrogen as an environmentally friendly and renewable fuel with high-energy density. This approach requires the development of appropriate photoelectrode materials and substrates, which are low-cost and applicable for the fabrication of large area electrodes. In this work, hematite photoelectrodes are grown by aerosol assisted chemical vapour deposition (AA-CVD) onto highly-conductive and bulk porous SnO2 (Sb-doped) ceramic substrates. For such photoelectrodes, the photocurrent density of 2.8 mA cm-2 is achieved in aqueous 0.1 M NaOH under blue LED illumination (λ = 455 nm; 198 mW cm-2) at 1.23 V vs. RHE (reversible hydrogen electrode). This relatively good photoelectrochemical performance of the photoelectrode is achieved despite the simple fabrication process. Good performance is suggested to be related to the three-dimensional morphology of the porous ceramic substrate resulting in excellent light-driven charge carrier harvesting. The porosity of the ceramic substrate allows growth of the photoactive layer (SnO2-grains covered by hematite) to a depth of some micrometers, whereas the thickness of Fe2O3-coating on individual grains is only about 100–150 nm. This architecture of the photoactive layer assures a good light absorption and it creates favourable conditions for charge separation and transport.</p

Hematite photoelectrodes grown on porous CuO–Sb₂O₅–SnO₂ ceramics for photoelectrochemical water splitting

Photoelectrodes capable of cost-effective hydrogen production on a large scale, via photoelectrochemical water splitting under solar light, could offer an elegant solution to many current problems of humankind caused by over-reliance on fossil fuels and the resulting environmental pollution. The search and design of low-cost photoelectrode materials and substrates for practical applications are required. In this work, unmodified hematite photoanodes grown by metal-organic chemical vapor deposition (MO-CVD) onto CuO–Sb2O5–SnO2 ceramic substrates are reported. The deposition time of hematite precursor varied between 10 min, 60 min, and 90 min. The photoanode grown for 60 min exhibits the highest photocurrent density recorded at 1.23 V vs RHE (reversible hydrogen electrode): 4.79 mA/cm2 under blue light of Thorlabs LED M455L2 (455 nm), 0.41 mA/cm2 under the radiation of the real sun in Mexico, and 0.38 mA/cm2 under AM1.5G solar simulator conditions. The high porosity of CuO–Sb2O5–SnO2 ceramics permits the permeation of the hematite precursor into the substrate bulk, which results in 3D-growth of a thin Fe2O3-coating (50 nm or less) on conductive SnO2-grains in the ceramics to a depth of ca. 5 μm. The thick photocatalytic layer (SnO2-grains coated by hematite) of several micrometers assures a good light harvesting by the photoelectrode, while the nano-sized Fe2O3-films on conductive SnO2-grains is favorable for charge diffusion. This architecture of the photoelectrode results in good photoelectrochemical characteristics and is promising for further development.</p

A hematite photoelectrode grown on porous and conductive SnO₂ ceramics for solar-driven water splitting

Photoelectrochemical water splitting using solar energy is a highly promising technology to produce hydrogen as an environmentally friendly and renewable fuel with high-energy density. This approach requires the development of appropriate photoelectrode materials and substrates, which are low-cost and applicable for the fabrication of large area electrodes. In this work, hematite photoelectrodes are grown by aerosol assisted chemical vapour deposition (AA-CVD) onto highly-conductive and bulk porous SnO2 (Sb-doped) ceramic substrates. For such photoelectrodes, the photocurrent density of 2.8 mA cm-2 is achieved in aqueous 0.1 M NaOH under blue LED illumination (λ = 455 nm; 198 mW cm-2) at 1.23 V vs. RHE (reversible hydrogen electrode). This relatively good photoelectrochemical performance of the photoelectrode is achieved despite the simple fabrication process. Good performance is suggested to be related to the three-dimensional morphology of the porous ceramic substrate resulting in excellent light-driven charge carrier harvesting. The porosity of the ceramic substrate allows growth of the photoactive layer (SnO2-grains covered by hematite) to a depth of some micrometers, whereas the thickness of Fe2O3-coating on individual grains is only about 100–150 nm. This architecture of the photoactive layer assures a good light absorption and it creates favourable conditions for charge separation and transport.</p

Porous and conductive SnO2 ceramics as a promising nanostructured substrate to host photocatalytic hematite coatings: Towards low cost solar-driven water splitting

Commercially viable generation of “green” hydrogen fuel by solar-driven water splitting requires the design of low-cost photoelectrodes and photo-devices with high photoelectrochemical performance. In this regard, conductive and easily fabricated 3D-oxide ceramics with nanosized grains and high porosity are promising as a substrate with a large surface area to host photocatalytic coatings. To test this approach, hematite photoelectrodes have been grown by metal-organic chemical vapor deposition onto free-standing SnO2-based ceramics. The photoanodes formed onto Sb2O5-SnO2, CuO-Sb2O5-SnO2, and on MoO3-Sb2O5-SnO2 substrates in aqueous 1 M NaOH under 1 sun irradiation exhibit photocurrent densities of 0.44 mA/cm2, 0.56 mA/cm2, and 0.39 mA/cm2 at 1.23 V vs. RHE, respectively. The porosity of ceramics results in the 3D growth of a thin hematite coating on ceramic grains in the substrate to a depth of ca. 3 μm. The obtained photoelectrodes are discussed based on the data of photoelectrochemical measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Raman spectroscopy. Routes to improved performance are discussed

Hematite photoelectrodes grown on porous CuO–Sb₂O₅–SnO₂ ceramics for photoelectrochemical water splitting

Photoelectrodes capable of cost-effective hydrogen production on a large scale, via photoelectrochemical water splitting under solar light, could offer an elegant solution to many current problems of humankind caused by over-reliance on fossil fuels and the resulting environmental pollution. The search and design of low-cost photoelectrode materials and substrates for practical applications are required. In this work, unmodified hematite photoanodes grown by metal-organic chemical vapor deposition (MO-CVD) onto CuO–Sb2O5–SnO2 ceramic substrates are reported. The deposition time of hematite precursor varied between 10 min, 60 min, and 90 min. The photoanode grown for 60 min exhibits the highest photocurrent density recorded at 1.23 V vs RHE (reversible hydrogen electrode): 4.79 mA/cm2 under blue light of Thorlabs LED M455L2 (455 nm), 0.41 mA/cm2 under the radiation of the real sun in Mexico, and 0.38 mA/cm2 under AM1.5G solar simulator conditions. The high porosity of CuO–Sb2O5–SnO2 ceramics permits the permeation of the hematite precursor into the substrate bulk, which results in 3D-growth of a thin Fe2O3-coating (50 nm or less) on conductive SnO2-grains in the ceramics to a depth of ca. 5 μm. The thick photocatalytic layer (SnO2-grains coated by hematite) of several micrometers assures a good light harvesting by the photoelectrode, while the nano-sized Fe2O3-films on conductive SnO2-grains is favorable for charge diffusion. This architecture of the photoelectrode results in good photoelectrochemical characteristics and is promising for further development.</p