First-principles calculation of activity and selectivity of the partial oxidation of ethylene glycol on Fe(0 0 1), Co(0 0 0 1), and Ni(1 1 1)

To recycle ethylene glycol (HOCH₂CH₂OH) fuel in alkaline fuel cells, active and selective catalysts for partially oxidizing HOCH₂CH₂OH to glycolic acid (HOCH₂COOH) and oxalic acid ((COOH)₂) are required at the anode; in other words, complete oxidation of HOCH₂CH₂OH to CO₂ prevents ethylene glycol recycling. We investigate catalyst activity and selectivity for oxidizing HOCH₂CH₂OH to HOCH₂COOH on Fe(0 0 1), Co(0 001), and Ni(1 1 1) via first-principles calculations. We calculate the oxidation reaction path from HOCH₂CH₂OH to HOCH₂COOH without C–C bond dissociation to avoid CO₂ generation. Partial oxidation of HOCH₂CH₂OH to HOCH₂COOH without C–C bond dissociation proceeds as follows: O–H bond dissociation of HOCH₂CH₂OH to generate HOCH₂CH₂O; C–H bond dissociation of HOCH₂CH₂O to generate HOCH₂CHO; C–H bond dissociation of HOCH₂CHO to generate HOCH₂CO; and OH addition to HOCH₂CO to generate HOCH₂COOH. The activation energies for O–H bond dissociation of HOCH₂CH₂OH and C–H bond dissociation of HOCH₂CH₂O and HOCH₂CHO on Fe(0 0 1) are 20.2, 22.8, and 35.2 kcal/mol, respectively, which are the lowest of the three surfaces. Thus, Fe(0 0 1) is most active. To determine the selectivity, we compare the bond dissociation activation energies. The activation energies for C–C bond dissociation of HOCH₂CH₂OH and HOCH₂CH₂O on Fe(0 0 1) (66.7 and 39.5 kcal/mol, respectively) are higher than those for O–H bond dissociation of HOCH₂CH₂OH (20.2 kcal/mol) and C–H bond dissociation of HOCH₂CH₂O (22.8 kcal/mol), implying that the O–H bond of HOCH₂CH₂OH and C–H bond of HOCH₂CH₂O dissociate before the C–C bond dissociation during oxidation on Fe(0 0 1). In contrast, the activation energies for C–H and C–C bond dissociation of HOCH₂CHO (35.2 and 32.8 kcal/mol, respectively) are similar. The C–H and C–C bonds therefore dissociate during HOCH₂CHO oxidation. On Co(0 0 0 1) and Ni(1 1 1), the activation energies for C–C bond dissociation of HOCH₂CH₂O and HOCH₂CHO are lower than those for their C–H bond dissociation. Therefore, Fe(0 0 1) is more active and selective than Co(0 0 0 1) and Ni(1 1 1) for the partial oxidation of HOCH₂CH₂OH to HOCH₂COOH.