Effect of Electronic Conductivities of Iridium Oxide/Doped SnO2 Oxygen-Evolving Catalysts on the Polarization Properties in Proton Exchange Membrane Water Electrolysis

Abstract

We have developed IrOx/M-SnO2 (M = Nb, Ta, and Sb) anode catalysts, IrOx nanoparticles uniformly dispersed on M-SnO2 supports with fused-aggregate structures, which make it possible to evolve oxygen efficiently, even with a reduced amount of noble metal (Ir) in proton exchange membrane water electrolysis. Polarization properties of IrOx/M-SnO2 catalysts for the oxygen evolution reaction (OER) were examined at 80 °C in both 0.1 M HClO4 solution (half cell) and a single cell with a Nafion® membrane (thickness = 50 μm). While all catalysts exhibited similar OER activities in the half cell, the cell potential (Ecell) of the single cell was found to decrease with the increasing apparent conductivities (σapp, catalyst) of these catalysts: an Ecell of 1.61 V (voltage efficiency of 92%) at 1 A cm−2 was achieved in a single cell by the use of an IrOx/Sb-SnO2 anode (highest σapp, catalyst) with a low Ir-metal loading of 0.11 mg cm−2 and Pt supported on graphitized carbon black (Pt/GCB) as the cathode with 0.35 mg cm−2 of Pt loading. In addition to the reduction of the ohmic loss in the anode catalyst layer, the increased electronic conductivity contributed to decreasing the OER overpotential due to the effective utilization of the IrOx nanocatalysts on the M-SnO2 supports, which is an essential factor in improving the performance with low noble metal loadings.

Enhancing Iridium Nanoparticles’ Oxygen Evolution Reaction Activity and Stability by Adjusting the Coverage of Titanium Oxynitride Flakes on Reduced Graphene Oxide Nanoribbons’ Support

“…Yet the differences among supported samples cannot be adequately explained by smaller particle size and thus higher surface area. In addition, several other factors can be responsible for the differences, such as the effect of the support [21][22][23][24]46,56] or difference in Ir-oxide composition (hydrous iridium oxide is more active than the crystalline oxide, which is usually produced thermally). [17,69] Ir/low-TiON x /rGONRs and Ir/rGONRs samples have a very similar structure and composition, as seen from the XRD diffractograms (see the black curves on Figure 1c,d on the graphene-based nanoribbons (2.30 wt% Ti as determined by ICP-OES), a bit smaller average particle size determined with relatively large measurement error (2.3 ± 0.5 nm (Ir/rGONRs) < 3.4 ± 0.5 nm) and the presence of large Ir particles found in Ir/rGONRs (20 nm and more) but not in the Ir/low-TiON x /rGONRs (Figure S6, Supporting Information).…”

“…[56] In the case of tin support, doping of the support is also considered a good technique to improve conductivity. [22,55] However, Da Silva et al recently showed that this doping could have a negative impact on the stability of the catalyst. [57] For titanium oxide, exchanging oxide ions for nitride provides sufficient conductivity for electrochemical support, as shown in our previous publications.…”

Constructing Supports–Network with N–TiO2 Nanofibres for Highly Efficient Hydrogen–Production of PEM Electrolyzer

“…IrOx/Nb-SnO 2 synthesized by Ohno et al using the flame pyrolysis method showed a high cell potential of 1.91 V at 1 A cm −2 [15]. Recently, Ramani's group [16] prepared bifunctional Pt-IrO 2 /RuTiO 2 using the co-deposition method; Pt-IrO 2 /RuTiO 2 showed a cell potential of >2 V at 1.5 A cm −2 .…”

Immobilization of Ir(OH)3 Nanoparticles in Mesospaces of Al-SiO2 Nanoparticles Assembly to Enhance Stability for Photocatalytic Water Oxidation

“…Thus, water oxidation catalysis of various metal oxides and metal complexes has been investigated in the photocatalytic water oxidation system using a photosensitizer and a sacrificial electron acceptor such as tris(2,2 -bipyridine)ruthenium(II) ion ([Ru II (bpy) 3 ] 2+ ) and persulfate ion (S 2 O 8 2− ), respectively [8][9][10][11][12][13][14][15][16][17][18]. So far, iridium oxide or iridium hydroxide nanoparticles have been reported as the most promising water oxidation catalysts ( Figure 1a) [19][20][21][22][23][24][25][26][27][28]. However, iridium oxide or iridium hydroxide nanoparticles can be deactivated due to agglomeration under harsh reaction conditions.…”