High‐Efficiency Direct Ammonia Fuel Cells Based on BaZr_0.1Ce_0.7Y_0.2O_3−δ/Pd Oxide‐Metal Junctions

Abstract

natural power electricity without relying on fossil fuels, and thus a fierce development race is going on to make "clean hydrogen" economically and technologically viable. Advent of hydrogen economy, however, cannot be realized until technical issues related to hydrogen production, transportation, and a storage infrastructure are clear. Ammonia is a highly efficient hydrogen carrier since it can be easily liquefied to store and transport at room temperature, is widely available, is carbon-free, and has hydrogen capacity larger than the liquid hydrogen. [1][2][3][4] Hence, it is strongly motivated to utilize ammonia in fuel cells for the direct conversion of ammonia chemical energy to electricity in a high efficiency. The proton conducting ceramic fuel cells (PCFCs) using protonconducting oxide electrolytes, such as BaZr x Ce 0.8−x Y 0.2 O 3−δ, is promising as a direct ammonia type fuel cell operating at the intermediate temperature (IT) range (400-600 °C) for stationary applications. [4][5][6][7][8][9] Because water formation in PCFCs is mainly progressive at the cathode side, unlike solid oxide fuel cells (SOFCs), and therefore, mixing of the ammonia fuels into the exhaust water is precluded, thereby eliminating repurification of water exhaust and simplifying total systems. Moreover, formation of environmentally hazardous substances NO x at the anode is discouraged if the proton conductivity is much higher than the minor oxide ion conductivity.Although the resistivity and related activation energy of proton conductors are smaller than oxide ion conductors used in SOFCs, the performances of the current PCFCs, however, are far behind the SOFCs even with pure H 2 fuels because of large interfacial polarization due to a lack of suitable cathode [10][11][12][13][14] and the deteriorated microstructural electrolyte. [15][16][17][18] Meanwhile, exceptionally high power output has been reported in the IT range for hydrogen membrane fuel cell (HMFC), [19][20][21][22][23] which comprises a thin proton conducting ceramic electrolyte supported on a dense hydrogen permeable metal anode with the anode reactions driven by separation of the monoatomic hydrogen dissolves into protons and electrons at electrolyte/ nonporous-anode solid-solid interfaces (Figure 1a). Regardless of its simple cell structure, the HMFC based on BaCe 0.8 Y 0.2 O 3 (BCY) thin film and Pd foil has achieved the maximum power density of 1.4 W cm −2 at 600 °C, [19,20] which is still higher than the average performances of recently reported highly efficiency PCFCs at the temperatures. [24][25][26][27] Here, we report on the highly

Recent progress in ammonia fuel cells and their potential applications

“…(a) Ammonia conversion percentages over different cermets in the presence of 100 % ammonia (b) fuel cell performance of a Ni-BCZY|BCY20|BCY20-LSCF at 550-700 o C using 66.7 % NH3-33.3 % Ar or 60.0 % H2-40.0 % Ar as the anodic gas and O2 as the cathodic gas.Temperature dependent effects have also recently been reported by Aoki et al, who employed a fuel cell utilizing a Pd anode, BZCY electrolyte and La0.6Sr0.4Fe0.8Co0.2O3 (LSFC) cathode, with both ammonia and hydrogen as the anodic fuel 121. The peak power density obtained at 450 o C was 71 mWcm -2 when operated with ammonia.…”

A New Pd Doped Proton Conducting Perovskite Oxide with Multiple Functionalities for Efficient and Stable Power Generation from Ammonia at Reduced Temperatures

“…Figure 6c gives a comparison of the performance of the Pd‐doped cell with several other ammonia‐fueled SOFCs as reported in literatures, where some special operation conditions are marked inside. [ 27–34 ] Obviously, the Pd‐doped single cell shows excellent performance in the PPDs and open circuit voltage (OCV).…”

“…a) I – V , I – P curves and b) EIS plots of PCFC with the configuration of Ni−BZCYYbPd anode, BZCYYbPd electrolyte, and BCFZY cathode in NH 3 from 650 to 550 °C. c) Summary of some literatures for NH 3 ‐fuel SOFCs at 600 °C with several special cases marked (■Ni‐Gd 0.2 Ce 0.8 O 1.9 (CGO)|BaCe 0.8 Gd 0.2 O 3− δ | Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3− δ (BSCF) + CGO, [ 27 ] ●Ni‐BaCe 0.75 Y 0.25 O 3− δ |BaCe 0.9 Y 0.1 O 3− δ |Sm 0.5 Sr 0.5 CoO 3− δ , [ 28 ] ▲Ni‐BaZr 0.1 Ce 0.7 Y 0.2 O 3− δ (BZCY)|BZCY|BSCF, [ 29 ] ▼Ni‐BaCe 0.8 Sm 0.2 O 3− δ (BCS)|BCS|BSCF+BCS, [ 30 ] ◆Pd foil|BZCY|La 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3− δ , [ 31 ] ◄Ni‐Sm 0.2 Ce 0.8 O 1.9 (SDC)|SDC|BSCF, [ 32 ] ►Ni‐BaCe 0.9 Nb 0.1 O 3− δ (BCN)|BCN|La 0.5 Sr 0.5 CoO 3− δ +BCN, [ 33 ] □Fe/Ni‐Y 0.16 Zr 0.92 O 2.08 (YSZ) |Sc 0.1 Zr 0.9 O 1.95 |La 0.7 Sr 0.2 MnO 3− δ , [ 34 ] △Ni−BZCYYb|BZCYYb|BCFZY (This work), ▽Ni−BZCYYbPd|BZCYYb|BCFZY (This work), ★ Ni−BZCYYbPd|BZCYYbPd|BCFZY (This work)). d) Operational stability of the single cell with Ni−BZCYYbPd anode and BZCYYbPd electrolyte operated at 550 °C on H 2 and NH 3 fuels under a current density of 0.2 A cm –2 .…”

High Diffusion Permeability of Anion-Exchange Membranes for Ammonium Chloride: Experiment and Modeling

“…Therefore, the ammonia recuperation from wastewater is a promising source of ammonia. In addition, ammonia salts have significant application potential for carbon-free energy storage and electrical power generation [ 10 , 11 , 12 , 13 ].…”