Dry Hydrogen Production in a Tandem Critical Raw Material-Free Water Photoelectrolysis Cell Using a Hydrophobic Gas-Diffusion Backing Layer

Abstract

A photoelectrochemical tandem cell (PEC) based on a cathodic hydrophobic gas-diffusion backing layer was developed to produce dry hydrogen from solar driven water splitting. The cell consisted of low cost and non-critical raw materials (CRMs). A relatively high-energy gap (2.1 eV) hematite-based photoanode and a low energy gap (1.2 eV) cupric oxide photocathode were deposited on a fluorine-doped tin oxide glass (FTO) and a hydrophobic carbonaceous substrate, respectively. The cell was illuminated from the anode. The electrolyte separator consisted of a transparent hydrophilic anionic solid polymer membrane allowing higher wavelengths not absorbed by the photoanode to be transmitted to the photocathode. To enhance the oxygen evolution rate, a NiFeOX surface promoter was deposited on the anodic semiconductor surface. To investigate the role of the cathodic backing layer, waterproofing and electrical conductivity properties were studied. Two different porous carbonaceous gas diffusion layers were tested (Spectracarb® and Sigracet®). These were also subjected to additional hydrophobisation procedures. The Sigracet 35BC® showed appropriate ex-situ properties for various wettability grades and it was selected as a cathodic substrate for the PEC. The enthalpic and throughput efficiency characteristics were determined, and the results compared to a conventional FTO glass-based cathode substrate. A throughput efficiency of 2% was achieved for the cell based on the hydrophobic backing layer, under a voltage bias of about 0.6 V, compared to 1% for the conventional cell. For the best configuration, an endurance test was carried out under operative conditions. The cells were electrochemically characterised by linear polarisation tests and impedance spectroscopy measurements. X-Ray Diffraction (XRD) patterns and Scanning Electron Microscopy (SEM) micrographs were analysed to assess the structure and morphology of the investigated materials.

Water Splitting with Enhanced Efficiency Using a Nickel-Based Co-Catalyst at a Cupric Oxide Photocathode

“…As shown in Figure 1 and in our previous papers [18,19], an n-type Titanium-doped hematite photoanode is characterized by a dark orange color corresponding to a UV/vis absorption edge below 600 nm. The support, herein represented by a drilled transparent conductive oxide (TCO), is designed to permit both the water flow inside the scalable photoelectrochemical cell and the escape of the oxygen produced by water splitting.…”

Anionic Exchange Membrane for Photo-Electrolysis Application

“…A good durability of anionic membrane-based-tandem cell was demonstrated in our previous work [ 26 , 27 ] by means of chrono-amperometric tests at −0.6 V and −0.8 V for 10 h in a proper hydrated environment. Moreover, in these recent activities, a step change in efficiency was achieved passing from FTO to GDL cathode substrate.…”

“…The PEC components were the following: (i) Photoanode based on titanium-doped hematite deposited over FTO glass; (ii) an anionic membrane FAA-3 in hydroxide form as the electrolyte [ 25 , 26 ]; (iii) photocathode based on copper oxide deposited on a Sigracet 35BC (SGL Carbon) substrate (previously hydrophobized with fluorinated ethylene propylene, FEP, at a loading of 7 wt.%) [ 27 ]; (iv) the ionomer dispersion was deposited over the photoelectrodes and after drying a conditioning step in 1 M KOH for 1 h was carried out.…”

“…The tandem PEC cell (1 cm 2 ) was assembled taking into account the best results obtained presently by our group as published in a recent paper [ 27 ]. The anionic membrane in hydroxide form (FAA3-50) was assembled between photoanode (Ti-doped hematite + ionomer) and photocathode (CuO/GDL + ionomer), as depicted in Figure 1 and described in previous papers [ 25 , 26 ].…”

“…As shown in Figure 1 , photoelectrodes are based on earth-abundant metal oxides such as α-Fe 2 O 3 (hematite) at the photoanode (PA), supported on fluorine tin oxide (FTO) substrate and CuO at the photocathode (PC) deposited on a gas diffusion layer (GDL) [ 27 ]. The polymer-electrolyte approach requires an effective interfacial contact between polymer-electrolyte and photoelectrodes able to permit an efficient ionic percolation.…”