Highly Active and Stable Cobalt-Free Hafnium-doped SrFe_0.9Hf_0.1O_3−δ Perovskite Cathode for Solid Oxide Fuel Cells

Abstract

Sluggish oxygen reduction reaction (ORR) kinetics and chemical instability of cathode materials hinder the practical application of solid oxide fuel cells (SOFCs).Here we report a Co-free Hf-doped SrFe 0.9 Hf 0.1 O 3−δ (SFHf) perovskite oxide as a potential cathode focusing on enhancing the ORR activity and chemical stability. We find that SFHf exhibits a high ORR activity, stable cubic crystal structure, and improved chemical stability toward CO 2 poisoning compared to undoped SrFeO 3−δ . The SFHf cathode has a polarization area-specific resistance as low as 0.193 Ω cm 2 at 600 °C in a SFHf|Sm 0.2 Ce 0.8 O 1.9 (SDC)|SFHf symmetrical cell and has a maximum power density as high as 1.94 W cm −2 at 700 °C in an anode-supported fuel cell (Ni+(ZrO 2 ) 0.92 (Y 2 O 3 ) 0.08 (YSZ)| YSZ|SDC|SFHf). The ORR activity maintains stable for a period of 120 h in air and in CO 2 -containing atmosphere. The attractive ORR activity is attributed to the moderate concentration of oxygen vacancy and electrical conductivity, as well as the fast oxygen kinetics at the operation temperature. The improved chemical stability is related to the doping of the redox-inactive Hf cation in the Fe site of SrFeO 3−δ by decreasing oxygen vacancy concentration and increasing metal−oxygen bond energy. This work proposes an effective strategy in the design of highly active and stable cathodes for SOFCs.

Unveiling Lithium Roles in Cobalt‐Free Cathodes for Efficient Oxygen Reduction Reaction below 600 °C

“…[3][4] However, sluggish oxygen reduction reaction (ORR) kinetics of the cathode in the IT range severely decreases power density. [16][17][18][19] The cubic SF structure can be stabilized with rare earth metals such as Bi 3 + , Sm 3 + , La 3 + at the A-site (Sr-site) and transition metals such as Ti 3 + , Mn 3 + , Ta 5 + , Nb 5 + , Hf 4 + , W 5 + , etc. [6][7][8][9][10][11][12] High MIECs can extend the ORR active sites to the entire cathode surface, significantly improving the catalytic activity of the cathode materials at reduced temperature.…”

“…[5] Cobalt-containing perovskite oxides such as SrCo 0.8 Nb 0.1 Ta 0.1 O 3-δ have attracted immense research interest as potential IT-SOFC cathodes because of their high mixed ionic and electronic conductivities (MIECs). [19][20][21][22][23] However, because of their lower MIECs SF-based cathodes normally exhibit a lower ORR activity than Co-based cathodes in the IT range. However, the high cost of cobalt, mismatched thermal expansion coefficients (TECs) with ceria-based electrolytes, and chemical incompatibility with zirconium-based electrolytes are the major concerns for the practical application of cobalt-containing perovskites in IT-SOFCs.…”

“…The high natural abundance of iron means they are relatively inexpensive and have a good thermal expansion match with the electrolytes. [16][17][18][19] The cubic SF structure can be stabilized with rare earth metals such as Bi 3 + , Sm 3 + , La 3 + at the A-site (Sr-site) and transition metals such as Ti 3 + , Mn 3 + , Ta 5 + , Nb 5 + , Hf 4 + , W 5 + , etc. at the B-site (Fe-site).…”

“…at the B-site (Fe-site). [19][20][21][22][23] However, because of their lower MIECs SF-based cathodes normally exhibit a lower ORR activity than Co-based cathodes in the IT range. [24][25] To circumvent these challenges, charge imbalance could be introduced at the A-site through incorporating lowvalent cations such as alkali metals.…”

Selective Partial Substitution of B‐Site with Phosphorus in Perovskite Electrocatalysts for Highly Efficient Oxygen Evolution Reaction

“…Among many candidates for oxygen electrocatalysis, perovskite oxides have gained increased attention in recent years thanks to the outstanding merits of the tunable structure, the employment of earth‐abundant elements, and the facile preparation process . Normally, perovskite oxides have a general formula of ABO 3 , wherein the A‐site is generally occupied by rare‐earth metal or alkaline‐earth metal, and the B‐site is generally took up by transition metal .…”