Enhanced Photoelectrochemical Water Splitting at Hematite Photoanodes by Effect of a NiFe-Oxide co-Catalyst

Abstract

Tandem photoelectrochemical cells (PECs), made up of a solid electrolyte membrane between two low-cost photoelectrodes, were investigated to produce “green” hydrogen by exploiting renewable solar energy. The assembly of the PEC consisted of an anionic solid polymer electrolyte membrane (gas separator) clamped between an n-type Fe2O3 photoanode and a p-type CuO photocathode. The semiconductors were deposited on fluorine-doped tin oxide (FTO) transparent substrates and the cell was investigated with the hematite surface directly exposed to a solar simulator. Ionomer dispersions obtained from the dissolution of commercial polymers in the appropriate solvents were employed as an ionic interface with the photoelectrodes. Thus, the overall photoelectrochemical water splitting occurred in two membrane-separated compartments, i.e., the oxygen evolution reaction (OER) at the anode and the hydrogen evolution reaction (HER) at the cathode. A cost-effective NiFeOx co-catalyst was deposited on the hematite photoanode surface and investigated as a surface catalytic enhancer in order to improve the OER kinetics, this reaction being the rate-determining step of the entire process. The co-catalyst was compared with other well-known OER electrocatalysts such as La0.6Sr0.4Fe0.8CoO3 (LSFCO) perovskite and IrRuOx. The Ni-Fe oxide was the most promising co-catalyst for the oxygen evolution in the anionic environment in terms of an enhanced PEC photocurrent and efficiency. The materials were physico-chemically characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM).

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 ]. The sandwiched cell was clamped at the sides providing a 0.25 cm 2 active area.…”

“…This separation for polymer-electrolyte membrane fuel cells (PEMFCs) and their subcategories [ 19 , 20 , 21 , 22 ] has been known for many years whereas the employment of a solid-membrane electrolyte has been less studied for PEC applications [ 23 , 24 ]. Its implementation in a cost-effective tandem PEC architecture, able to capture a significant portion of the solar irradiation, is structured as photoanode/membrane/photocathode and the working mechanism has been discussed in detail in some recent work [ 25 , 26 ].…”

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

“…The existence of several concerns related to the increasing energy demand and the related environmental crisis [1][2][3][4][5][6] indicates the need to identify innovative, effective and low cost solutions. Photoelectrochemical water splitting (PWS) [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] is recognised as a promising strategy and it attracts particular interest for storing solar energy into the chemical bonds of hydrogen as fuel [26][27][28], which can be further utilised in fuel cells [29][30][31][32][33][34], internal combustion engines and to progressively decarbonize industrial processes [35][36][37][38][39].…”