Cobalt-Doped Carbon Nitride Frameworks Obtained from Calcined Aromatic Polyimines as Cathode Catalyst of Anion Exchange Membrane Fuel Cells

Abstract

Cobalt-doped carbon nitride frameworks (CoNC) were prepared from the calcination of Co-chelated aromatic polyimines (APIM) synthesized from stepwise polymerization of p-phenylene diamine (PDA) and o-phthalaldehyde (OPAl) via Schiff base reactions in the presence of cobalt (II) chloride. The Co-chelated APIM (Co-APIM) precursor converted to CoNC after calcination in two-step heating with the second step performed at 100 °C lower than the first one. The CoNCs demonstrated that its Co, N-co-doped carbonaceous framework contained both graphene and carbon nanotube, as characterized by X-ray diffraction pattern, Raman spectra, and TEM micropictures. CoNCs also revealed a significant ORR peak in the current–voltage polarization cycle and a higher O2 reduction current than that of commercial Pt/C in a linear scanning voltage test in O2-saturated KOH(aq). The calculated e-transferred number even reaches 3.94 in KOH(aq) for the CoNC1000A900 cathode catalyst, which has the highest BET surface area of 393.94 m2 g−1. Single cells of anion exchange membrane fuel cells (AEMFCs) are fabricated using different CoNCs as the cathode catalysts, and CoNC1000A900 demonstrates a peak power density of 374.3 compared to the 334.7 mW cm−2 obtained from the single cell using Pt/C as the cathode catalyst.

2,6-Diaminopyridine-Based Polyurea as an ORR Electrocatalyst of an Anion Exchange Membrane Fuel Cell

“…We demonstrated in Equation (1) that one O 2 molecule and one water molecule can be fully reduced to four hydroxyl ions (OH − ) by cathode catalysts in an alkaline solution, following the 4e-pathway. However, HO 2 − is an unavoidable intermediate by-product [ 30 , 31 , 32 , 33 , 40 ] due to the incomplete ORR (oxygen reduction reaction) in an alkaline medium (Equation (2)). Based on Equation (2), the reduction reaction can continue further after the supply of two additional electrons, the so-called 2e-pathway (Equation (2) plus Equation (3)).…”

“…To avoid the trouble of preparing the macrocyclic structure and the addition of a carbon matrix such as carbon black (CB), we have prepared many nitrogen-containing polymers (N polymers). The N polymers can chelate with cobalt ions (Co(II)) and calcine to create a Co–N–C structure [ 30 , 31 , 32 , 33 ] without the addition of any CB.…”

Cobalt-Based Cathode Catalysts for Oxygen-Reduction Reaction in an Anion Exchange Membrane Fuel Cell

“…The total volume of CoNC-1000A-900 is almost twice as much as that of CoNC-800A-700 and all above 1 cm 3 , indicating more volume developing with increasing temperature. The contribution of the additional volume might result from the breaking of the aliphatic carbon single chain of DETA since the BET SA is below 400 m 2 g −1 , and total volume is always below 1 cm 3 if Co, N-doped polyimine is prepared from an aromatic diamine monomer [ 15 , 16 ]. In other words, to replace phenylene diamine with DETA in the preparation of Co-PIM not only can chelate more Co ions by the additional amine but also provide catalysts with higher SA and volume after calcination, matching with the original purpose described in the introduction section.…”

“…The performances of various non-precious metal catalysts are listed in Table 5 . [ 15 , 16 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 ] Obviously, the P max values depend on the weights of the catalysts in both electrodes and types of anode catalysts as well. This work demonstrates high P max with only 20% Pt/C in the anode, compared to those using expensive Ru-Pt/C.…”

“…[ 13 , 14 ]. We have been investigating chelating iron or cobalt ions with nitrogen-containing (N-containing) compounds, which were then calcined to become metal–organic frameworks as cathode catalysts for proton exchange membranes (PEMs) or anion exchange membrane fuel cells (AEMFCs) [ 15 , 16 , 17 , 18 ]. In this study, we needed more robust Co ion absorbers, which can be converted into Co-doped nitrogen-containing carbonaceous composites (Co-N-C) as cathode catalysts of AEMFCs.…”