The preferred adsorption sites and catalytic mechanism of FCC_CoFeGaNiZn multi-principal element alloy for oxygen evolution reaction catalysis based on site preference of constituent atom on sublattice

Abstract

The origin of distinguished oxygen evolution reaction (OER) catalytic properties of multi-principal element alloys (MPEAs) is not clear yet due to the rich surface-active sites may exist in MPEAs composed of multiple types of elements, which may bring complex catalytic environment. In this work, four main steps were carried out using computational materials science. The atom distribution of bulk MPEAs was constructed firstly based on the previously predicted site preference of atoms occupying sublattices, which is beyond the traditional hypothesis that the atom distributing randomly on the whole lattice. Then the (111) close-packed surface slab of CoFeGaNiZn MPEA was obtained by cleaving the bulk structure. Subsequently, the OER processes were systematically explored by calculating the free energy change of intermediates *OH, *O, and *OOH at 171 adsorption sites on the (111) surface. Finally, the oxygen evolution reaction catalytic mechanism and its site preference behavior of FCC_CoFeGaNiZn MPEA were discussed in detail. The results show that atoms have obvious site preference, which deviating the ideal randomly distribution, especially Co, Fe and Zn atoms always prefer to 3c sublattice at all temperature, Ga atoms tend to favor 1a sublattice, and the site preferences of Ni atoms and Ga atoms are affected by the heat treatment temperature. At 1273 K, the site occupying configuration is (Co0.0246Fe0.01680Ga0.4550Ni0.4990Zn0.0046)1a (Co0.2580Fe0.2610Ga0.1150Ni0.1000Zn0.2650)3c. The (111) surface of FCC_CoFeGaNiZn MPEA was based on the site occupying configuration at 1273 K, and it was then supposed to quenched to ground state to simulate the experimental status in the available literature. Since *O at hollow sites transforms into *OOH at a higher overpotential, hollow sites may be poisoning surface sites. Three intermediates are found to primarily participate in the catalytic reaction on top sites. In addition, there are no scaling relationships between ΔE*OH and ΔE*O for CoFeGaNiZn MPEA, even for the same type of top sites. It is noteworthy that an average overpotential of 0.349 V was predicted by considering the combinations of three intermediate-tendency elements, which is in better agreement with the experimental overpotential of 0.37 V at 10 mA/cm2 current density than the overpotential of 0.28 V based on the special quasirandom structures (SQS). Current intensive explorations bring new insights into the OER catalytic mechanism of the preferred adsorption sites of MPEAs based on the reasonable consideration concerning the atoms distributing configuration involving the exact site preference of the constituent metallic atoms on the sublattice.