Abstract
Glycerol is a byproduct of biodiesel production and, as such, it is of limited economic value. By means of electrooxidation, glycerol can be used as a feedstock for scalable hydrogen production, in addition to conversion to value-added products. The development of novel and efficient catalytic electrode materials for the anodic side of the reaction is a key towards a hydrogen-based energy economy. In the present study, a computational screening protocol combining DFT, scaling relations, and microkinetic modeling allows for a rational selection of novel catalysts that can deliver efficient glycerol electrooxidation, low cost of production, and environmental sustainability. Activity and chemical selectivity towards hydrogen production on pure metal catalysts is discussed in terms of volcano-shaped plots. We find that the selectivity in the glycerol oxidation reaction is influenced by a different energy landscape when in the presence of water and best classified by a comparison of OH and CH bond-breaking barriers. In addition, we screened 3570 bi-metallic catalysts in the AB (L10) and A3B (L12) ordered structures for activity, stability, price, and toxicity. By filtering based on the criteria for toxicity, resistance to oxidation, miscibility, and price, we have identified 5 L10 structured catalysts (AgPd, AuPd, PtSb, CuPt, and AgPt) and 20 L12 catalysts (Ga3Ta, In3Ta, Ir3W, Ir3Mo, Cu3Pt, Ir3Ta, Ir3Re, Pd3Bi, Pd3Cu, Pd3W, Pd3Co, Pd3Sn, Pd3Mo, Pd3Ag, Pd3Ga, Pd3Ta, Au3Ru, Pd3In, Au3Ir, and Pd3Au) that are all predicted to show high activity. We also identify an additional 37 L10 and 92 L12 structured electrocatalysts with an anticipated medium-high activity.
Highlights
Glycerol is a common side-product in the biodiesel industry providing an abundant renewable feedstock that can be used for the synthesis of higher-value chemicals, as well as for the production of hydrogen [1,2]
For each pair of (O∗, C∗) adsorption energies on a two-dimensional grid covering the range relevant for the metals of the present study, we solve the microkinetic modelling [66] (MKM), which results in so-called volcano plots that map out the activity, coverage, and selectivity as function of the chosen descriptors
We have developed free energy linear-scaling relations for adsorption energies and transition states for reported intermediates and products associated with the first two deprotonation steps in glycerol electrooxidation
Summary
Glycerol is a common side-product in the biodiesel industry providing an abundant renewable feedstock that can be used for the synthesis of higher-value chemicals, as well as for the production of hydrogen [1,2]. A few works report on catalysts composed of non-precious metals like Ni, Fe, Co, and Cu (e.g., NiFe [60], NiCo [60,61,62], and NiCu [61]). These are reported to oxidize to oxyhydroxides (i.e., NiOOH, CoOOH, and FeOOH), requiring rather high potential for GEV. C–C bond cleavage of the glycerol molecule is enhanced, producing lower yield of the desired C3 products when compared to the pure metals [60,61,62]
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