Micro‐/Nanohoneycomb Solid Oxide Electrolysis Cell Anodes with Ultralarge Current Tolerance

Abstract

This efficiency is significantly higher than that of traditional chemical approaches such as CO 2 hydrogenation or reforming. [14] In addition, operations at high temperatures can achieve larger cur rent densities due to lowering resistances, increasing productivity and reducing system size/cost.Although SOEC electrodes with perov skite structures (e.g., La 0.8 Sr 0.2 CoO 3−δ ) have the potential to tolerate current density as high as 5 A cm −2 (see the Sup porting Information for details), prac tical electrode performances degrade quickly, even at low current densities (e.g., 500 mA cm −2 ). [15,16] Such fading is mainly attributed to intensified current densi ties, causing anode delamination due to extremely high oxygen partial pressures (P O2 ) at the anode-electrolyte interface. [17,18] Notably, compared with reverse devices (solid oxide fuel cells, SOFCs), the P O2 at the anode-electrolyte interface for SOECs are commonly several times higher, [19] and further increases more than 100 times under a large current density (>1 A cm −2 ). [20] Therefore, performance degradation is even more serious for SOECs. Such high P O2 can be attributed to inherent structural defects. Traditionally, using perovskite materials (e.g., La 0.6 Sr 0.4 CoO 3±δ (LSC)) as precursors, SOEC anodes prepared by screenprinting or wet powder spraying methods [21] mainly possess spongelike structures (as shown in Figure 1a, traditional electrode LSC (TELSC) is illustrated as an example). Such spongelike anodes typically possess enor mous pores distributed randomly in space and varied widely in size. [22] Although the inherent electronic and ionic conduc tivity provided by LSC should be sufficient for operations at high temperatures (e.g., 800 °C) and large current densities (e.g., 1-2 A cm −2 ), the properties advantages are greatly lim ited by the spongelike structure due to the sluggish oxygen generation and release kinetics. Specifically, here sluggish oxygen generation is ascribed to the limited interface areas for oxygen evolution reactions (OERs). [23,24] And the poor oxygen release is caused from tortuosity factors (typically, >3 [25] ), low porosities (typically, <30%), [26] and even blocked tunnels, thus suffocating generated gases and subsequently causing anode delamination at high current densities. [22] Currently, hierarchical micro/nanostructures with well oriented nanoarrays have shown superwetting behaviors in aqueous electrolyte environments and demonstrated high efficiencies for electrolyzing (e.g., water splitting and fuel cells). [27,28] Studies in medium or high temperature systems As a clean, efficient, and promising energy conversion device, solid oxide electrolysis cell (SOEC), which can achieve transformation from electricity to chemical fuels, has captured worldwide attention. A novel biomimetic honeycomb SOEC anode with super low tortuosity factor (≈1), ground-breaking porosity (≈75%), and high structural strength, has been successfully fabricated by freeze casting and infiltrating. This honeycomb anode demonstrat...

Robust Anode‐Supported Cells with Fast Oxygen Release Channels for Efficient and Stable CO2 Electrolysis at Ultrahigh Current Densities

“…There are a few studies reporting electrolysis stability at a current density of 2.0 A cm −2 or above. Compared with these results (Figure S12, Supporting Information), the electrolysis over the anode‐supported SOECs demonstrated outstanding stability as well as similar initial cell voltage as conventional cathode‐supported SOECs, [ 12,13,15,43,44 ] although the electrolysis over the cathode‐supported SOECs can become more stable as the current density was decreased. [ 12 ] These results were tested during steam electrolysis or co‐electrolysis of steam and CO 2 , and it is hence expected that lower electrolysis voltages are required for the steam electrolysis or co‐electrolysis over the anode‐supported SOECs in this study.…”

“…As mentioned, the accumulation of high gas pressure within the anode layer for cathode‐supported SOECs during high current electrolysis is due to the not in‐time release of produced oxygen which creates the mechanical force that makes the anode delaminate from the electrolyte surface. It suggests that if the oxygen can efficiently release from the anode, the pressure increase inside the anode layer will also be greatly mediated, [ 15 ] and improved cell stability is then to be expected. As presented in Figure a,b, the graded channel structure is ideal for achieving the fast oxygen evolution and release: small channels in the reaction zone near the anode‐electrolyte interface provide a large surface for the oxygen evolution; the graded channel structure facilitates the oxygen collection and release to the anode's surface.…”

“…The anode‐supported SOEC achieved a low electrode polarization resistance of 0.018 Ω cm 2 at 800 °C, which is even comparable with that (0.0094 Ω cm 2 ) of a cell with an infiltrated anode and Pt cathode. [ 15 ] Impressively, there is no concentration polarization observed at a current density as high as −3.5 A cm −2 .…”

“…A study has attempted to address the problem of anode delamination in cathode‐supported SOECs, [ 15 ] in which a (Y 2 O 3 ) 0.08 Zr 0.92 O 2 (YSZ) anode scaffold was adhered to a prepared YSZ electrolyte layer by layer with a YSZ paste and subsequently co‐sintered at a high temperature of 1400 °C, resulting in a strong adhesion between the two layers. The YSZ anode scaffold prepared by freeze‐casting had a honeycomb structure with straight channels, which effectively improved oxygen release from the interface to the anode surface.…”

A Novel Solid Oxide Electrolysis Cell with Micro‐/Nano Channel Anode for Electrolysis at Ultra‐High Current Density over 5 A cm−2

“…Moreover, the temperature dependance of the R p is shown in Figure 3b. [19,[28][29][30] The R p of the MC-anode is one third to one fiftieth lower than those of several reported SL-anodes at 800 °C, indicating such MC-anode has obviously [13] SL LSC-GDC (Gd 0.2 Ce 0.8 O 1.9 ) anode, [29] and SL LSC-SDC (Sm 0.2 Ce 0.8 O 2-δ ) anode. [30] c) Time dependance curve of overpotential of MC-anode and SL-anode under different current densities at 800 °C.…”