High-throughput compositional screening of PdxTi1–xHy and PdxNb1–xHy hydrides for CO2 reduction

Electrochemical experiments and theoretical calculations have shown that Pd-based metal hydrides can display good performance in the CO2 reduction reaction (CO2RR). To explore higher-performance catalysts, Pd-based alloy hydrides PdxM1–xHy are studied in this work. Our previous work on doped-PdH showed that doping Ti and Nb into PdH can improve the CO2RR activity, suggesting that the Pd alloy hydrides with better performance are likely to be found in the Pdx Ti1–xHy and PdxNb1–xHy phase space. However, the complex nature of the compositional and structural phase space that includes different compositions of alloy hydrides, different concentrations of the metal element and H of alloy hydrides, different adsorption sites, and different adsorbates, makes it intractable to screen out the stable and active PdxM1–xHy catalysts using density functional theory (DFT) calculation. Herein, an active learning cluster expansion (ALCE) surrogate model equipped with Monte Carlo simulated annealing (MCSA), a CO* filter and a kinetic model are used to identify promising Pdx Ti1–xHy and PdxNb1–xHy catalysts with high stability and superior activity. Finally, 24 stable and active candidates of Pdx Ti1–xHy and 6 active candidates of PdxNb1–xHy are found using our approach. Among them, the Pd0.23Ti0.77H, Pd0.19Ti0.81H0.94 and Pd0.17Nb0.83H0.25 display superior current densities of approximately 5.1, 5.1 and 4.6 μAcm−2 at −0.5V overpotential, respectively, which are significantly higher than that of PdH at 3.7 μAcm−2. Their free energy diagram shows that their HOCO* binding is not too weak, while their CO* binding is not too strong, resulting in enhanced activities. The statistical analysis shows that the binding energies are mainly contributed by the elements Ti/Nb and H. Hence, three candidates, Pd0.23Ti0.77H, Pd0.19Ti0.81H0.94, and Pd0.17Nb0.83H0.25, are recommended in this work.