Symmetrical Exsolution of Rh Nanoparticles in Solid Oxide Cells for Efficient Syngas Production from Greenhouse Gases

Abstract

Carbon dioxide and steam solid oxide co-electrolysis is a key technology for exploiting renewable electricity to generate syngas feedstock for the Fischer-Tropsch synthesis. The integration of this process with methane partial oxidation in a single cell can eliminate or even reverse the electrical power demands of co-electrolysis, while simultaneously producing syngas at industrially attractive H2/CO ratios. Nevertheless, this system is rather complex, and requires catalytically active and coke tolerant electrodes. Here, we report on a low-substitution rhodium-titanate perovskite (La0.43Ca0.37Rh0.06Ti0.94O3) electrode for the process, capable of exsolving high Rh nanoparticle populations, and assembled in a symmetrical solid oxide cell configuration. By introducing dry methane to the anode compartment, the electricity demands are impressively decreased, even allowing syngas and electricity cogeneration. To provide further insight on Rh nanoparticles role on methane-to-syngas conversion, we adjusted their size and population by altering the reduction temperature of the perovskite. Our results exemplify how the exsolution concept can be employed to efficiently exploit noble metals for activating low-reactivity greenhouse gases in challenging energy related applications.

Emergence and Future of Exsolved Materials

“…This of course poses additional requirements as to the exact conditions as far as the oxygen partial pressure (pO 2 ) of the gas, the temperature of the reduction as well as the ramping rate to the required temperature. [41] Depending on the materials studied it has been shown that high temperature leads to low particle population and larger particle size [33,42,43] while one can have an impact on the nature of the exsolved species by changing the type of the reducing gas (Figure 11). [22] For example, reduction under CO atmosphere could produce cubic particles while slightly humidified H 2 can lead to the exsolution of nanorods or even heterostructures.…”

Progress of Exsolved Metal Nanoparticles on Oxides as High Performance (Electro)Catalysts for the Conversion of Small Molecules

“…As shown in Table 4 , these reported exsolution materials include single metal particles composed of Ni, [ 68,115–122 ] Cu, [ 92 ] Co, [ 81 ] Fe, [ 135–137 ] and Rh. [ 108 ] Such materials also encompass alloys, such as Fe–Ni, [ 101,102,144,145 ] Ni–Cu, [ 105,152 ] Co–Ni, [ 150 ] and Co–Fe. [ 101,154–156 ] For the electrolysis of pure CO 2 gas, exsolution materials were generally used as the cathode electrodes of SOECs.…”

“…Besides water, some researchers put CH 4 gas into the anode to assist CO 2 electrolysis in SOECs. [ 105,108 ] This reaction combined CO 2 electrolysis (CO 2 + 2e − = CO + O 2− ) with CH 4 electrochemical oxidation (CH 4 + O 2− = CO + 2H 2 + 2e − ) in a simultaneous process. Lu et al.…”

Progress and Opportunities for Exsolution in Electrochemistry

“…An impressive application for exsolution electrodes is for the co-generation of valuable chemical products (CH 4 , CO, H 2 ) and electricity. Ru exsolution from La 0.43 Ca 0.37 Rh 0.06 Ti 0.94 O 3 was shown to be effective at co-electrolysis (where CO 2 and H 2 O are reduced to CO and H 2 at the cathode), CH 4 -assisted co electrolysis (where CH 4 is simultaneously oxidized to CO 2 and H 2 O at the anode via O 2− transport) and co-generation, where the reversible potential becomes negative and electricity and chemical products are produced together [52]. In addition to the examples cited above, a partial summary of the advancements made in the design of exsolution electrodes is given in Table 1.…”