Effect of Au and/or Mo Doping on the Development of Carbon and Sulfur Tolerant Anodes for SOFCs—A Short Review

Abstract

HIGHLIGHTS• The kinetics of CH 4 steam reforming and partial oxidation are determined by the oxidation rate of CH x adsorbed species • The modification of the Ni/YSZ and Ni/GDC with Au and/or Au-Mo results in differentiated structures of atomically dispersed Au and/or Au-Mo at the surface and the bulk of the Ni particles.• At lean S/C NiAu/YSZ selectively oxidizes electrochemically the catalytically produced H 2 and CO, while NiAu/GDC is selective to the direct partial electrochemical oxidation of CH 4 to CO and H 2.• The modified electrodes show significant tolerance to C formation.• Au-Mo modification enhances the intrinsic sulfur tolerance properties of Ni/GDC.The presented work is a short review of the research attempts from our group with collaborators, during the last 15 years, which had as main objective to study and improve the electrocatalytic performance of Ni-based electrode materials for the CH 4 Internal steam Reforming process (ISR.) in Solid Oxide Fuel Cells (SOFCs). In particular, NiO/YSZ and NiO/GDC anode powders were modified with Au and/or Mo nano-particles via different preparation methods. These efforts resulted in anode materials with high tolerance and improved electrocatalytic activity under both carbon forming and sulfur poisoning conditions. The most important findings are being reviewed and critical findings are being highlighted 50 as to stress the key differences in the electrocatalytic performance between Ni/YSZ and Ni/GDC. The possible effects of Au and/or Mo addition on the physicochemical and strucutral properties of the cermets are thoroughly discussed as well as active functional layers in the form of anode SOFC electrodes.

The promoting effect of Fe on Ni/ GDC for the Solid Oxide H 2 O electrolysis

“…12,13 Another promising approach in the field of high temperature Solid Oxide fuel cells is to promote the electrocatalytic activity of Ni-based electrodes, through the dispersion of small amounts of noble (eg, Pt, Pd, Rh, Ru, Au) or non-noble transition metal elements (eg, Sn, Cu, Mo, Bi). 9,14 There are also similar trends in the field of low temperature (liquid) water electrolysis applications, such as those recently published by K. S. Bhat and H. S. Nagaraja, who reported nickel chalcogenides 15 (sulfides, selenides and tellurides) as promising substitutes of the State of the Art (SoA) (Pt, IrO 2 , RuO 2 ) electrocatalysts, as well as formulations based on copper sulfidenickel sulfide arrays. 16 Albeit the status of modified Solid Oxide Ni-based fuel cell electrodes, the research level in the case of electrolysis is currently in progress.…”

Co-electrolysis of H2O and CO2 on exsolved Ni nanoparticles for efficient syngas generation at controllable H2/CO ratios

“…Table S1. [17,18,25], the observed values are slightly higher demonstrating the adequate activity of our cell. Table 1 cycles under steam and co-electrolysis conditions, in which a steady-state was always significantly increased for both electro-catalysts, indicating slower kinetics of the CO2 than H2O electrolysis.…”

“…In SOECs, Νi/YSZ cermets are most commonly employed as fuel electrode, due to their high ionic and electronic conductivity, as well as electro-catalytic activity for H2O/CO2 splitting [2,5,[12][13][14][15][16][17][18][19]. Nevertheless, Ni-based cermet electrodes have significant drawbacks, which include sensitivity to microstructure changes caused under redox conditions and susceptibility to impurities such as sulfur (typically present in the feed stream) and coking even under high steam concentrations [5,[20][21][22].…”

Experimental Clarification of the RWGS Reaction Effect in H2O/CO2 SOEC Co-Electrolysis Conditions

“…This means that the bonding strength of the adsorbed oxygen species, which result from H 2 O decomposition, may induce the re-oxidation of the electrode and finally the deactivation of the sample [46,53]. The H 2 O poisoning effect in electrolysis and co-electrolysis processes can also be correlated to the CH 4 poisoning effect in SOFC applications, where degradation is enhanced by the strong adsorption bond of CH 4 on the Ni surface [23,[42][43][44][45]54,55]. Thus, the stronger binding of the adsorbed oxygen species, which result from the catalytic dissociation of H 2 O ads , can similarly cause a poisoning effect on the Ni surface, leading to faster re-oxidation and finally deactivation of the sample [46,53].…”