Hydrogen is a clean source of energy when prepared from electrocatalytic water splitting driven by renewable energy sources such as solar or wind. However, electrocatalytic water splitting faces significant challenges in the form of energy losses due to kinetic barriers for the water reduction (hydrogen evolution reaction, HER) and water oxidation (oxygen evolution reaction, OER) processes. The state-of-the-art electrocatalysts including Pt (HER), RuO2 and IrO2 (OER) can reduce the kinetic barriers, but these catalysts suffer from scarcity and high cost of the metals. Therefore, there is a need to explore new materials made from inexpensive and earth-abundant elements that are able to perform water splitting processes efficiently and more cost-effectively. Transition metal phosphide (TMP) nanomaterials have recently shown promising catalytic activity towards water splitting processes. Ternary phase TMP nanoparticles made by combination of two earth-abundant transition metals (Ni2−xCoxP, Co2-xMnxP, Fe2−xMnxP) or an abundant metal with a noble metal (Ni2−xRuxP, Co2−xRhxP) have shown enhanced activity toward HER, OER or both processes, relative to binary phases. The enhanced activity is attributed to synergistic effects arising from the combination of two different metals with different activities and properties. Manganese containing materials are an attractive choice for performing OER catalysis as Mn plays an important role in O2 evolution by photosystem II. We have developed synthetic strategies to produce Co2-xMnxP (x≤1.4) nanoparticles and Fe2−xMnxP (0≤x≤0.9) nanorods, and both systems were active OER catalysts. Since Ni2P is an active catalyst for water splitting and Ni is less oxophilic than Fe, and Co, we hypothesized that Ni2-xMnxP may be more active and more stable towards OER relative to Co2-xMnxP and Fe2−xMnxP. Here, we present a synthetic route towards discrete nanoparticles of Ni2-xMnxP, along with composition-dependent studies of the catalytic activity and stability of Ni2-xMnxP nanomaterials with respect to the electrocatalytic OER process. These data will be discussed in the context of prior work on bimetallic manganese-based phosphides with a focus on elucidating the role of secondary metal on moderating catalytic function.

Synthesis of discrete nanoparticles of Ni2-xMnxP: Elucidating the role of the secondary metal in dictating the performance of ternary manganese phosphides for water oxidation electrocatalysis

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