The Active Center of Co–N–C Electrocatalysts for the Selective Reduction of CO₂ to CO Using a Nafion-H Electrolyte in the Gas Phase

Abstract

To contribute a solution for the global warming problem, the selective electrochemical reduction of CO 2 to CO was studied in the gas phase using a [CO 2 (g), Co–N–C cathode | Nafion-H | Pt/C anode, H 2 /water] system without using carbonate solutions. The Co–N–C electrocatalysts were synthesized by partial pyrolysis of precursors in inert gas, which were prepared from various N-bidentate ligands, Co(NO 3 ) 2 , and Ketjenblack (KB). The most active electrocatalyst was Co–(4,4′-dimethyl-2,2′-bipyridine)/KB pyrolyzed at 673 K, denoted Co–4,4′-dmbpy/KB(673K). A high performance of CO formation (331 μmol h –1 cm –2 , 217 TOF h –1 ) at 0.020 A cm –2 with 78% current efficiency was obtained at −0.75 V (SHE) and 273 K under strong acidic conditions of Nafion-H. Characterization studies using extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy–energy-dispersive X-ray (TEM-EDX), X-ray diffraction (XRD), and temperature-programmed desorption with mass spectrometry (TPD-MS) indicated the active site as Co coordinated with four N atoms bonding the surface of KB, abbreviated Co–N 4 –C x structure. A model of the reduction mechanism of CO 2 on the active site was proposed.

Pure Hydrogen Production by Aqueous Ethanol Electrolysis on Pt–Ru–O Anodes in a Solid Polymer Electrolyte Electrolysis Cell

“…Of course, the varying catalyst preparation and electrochemical test conditions also affect the observed catalytic activity for EOR but the performance and mechanism of Pt–Ru as a catalyst for EOR remain unclear. Utilization of the SPE electrolysis cell for H 2 production has many advantages over conventional electrolysis systems, for example, a lower terminal voltage, easy separation of the reactant from the electrolyte, and so on. − …”

A spherical multishell hollow carbon-based catalyst with a controllable N-species content for the oxygen reduction reaction in air-breathing cathode microbial fuel cells

“…in the S–Co–Ni/N–C- T catalysts, while S–Co/N–C-850 shifted by ∼0.18 eV (Co 2p3/2) and 0.19 eV (Co 2p3/2). 34,35 Homoplastically, the Ni 2p high-resolution XPS spectra in Fig. 5i show a shift to a lower B.E.…”

Electrochemical CO2 reduction in membrane-electrode assemblies

“…MEA CO 2 RR electrolyzers offer several advantages, compared with systems with flowing-electrolyte; therefore, recently researchers have developed electrolyte-free systems for efficient CO 2 RR. 32,[42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59] It has been reported that MEA (or zero-gap or fuel cell-like) systems show a lower resistance and cell potential due to the absence of electrolytes. In addition, pumping an electrolyte brings some complexities to the systems (e.g., pumping, purification of electrolyte, etc.…”

“…Production of CO by using CO-selective Au and Ag electrocatalysts has been the main application of MEA systems for CO 2 RR. 42,45,46,[48][49][50][51][52][53]62,63 31 Using CEMs results in an acidic environment on the cathode side, causing a severe hydrogen evolution reaction (HER), thereby, they used an alkaline ion-exchange membrane. As can be seen in Figure 3B, CO 2 RR occurs on Au (as the CO-selective electrocatalyst), deposited on an alkaline polymer electrolyte membrane coupled with oxygen reduction in the anode (IrO 2 ) with pure water.…”