Unraveling the Synergistic Mechanism of Bi-Functional Nickel–Iron Phosphides Catalysts for Overall Water Splitting

摘要

Ni–Fe bimetallic electrocatalysts are expected to replace existing preciousmetal catalysts for water splitting and achieve industrial applications dueto their high intrinsic activity and low cost. However, the mechanism bywhich Ni and Fe species synergistically enhance catalytic activity remainsobscure, which still needs further in-depth study. In this study, a highly activebi-functional electrocatalyst of Ni_2P/FeP heterostructures is constructed onFe foam (Ni_2P/FeP-FF), clearly illustrating the effect of Ni on Fe species foroxygen evolution reaction (OER) and revealing the true catalytic active phasefor hydrogen evolution reaction (HER). The Ni_2P/FeP-FF only needs overpotentialsof 217 and 42 mV to reach 10 mA cm~(?2) for OER and HER, respectively,exhibiting superior bi-functional activity for overall water splitting. The Ni canelevate the strength of FeO on Ni2P/FeP-FF surface and promote the formationof high-valence FeOOH phase during OER, thus enhancing OER performance.Based on first-principles calculations and Raman characterizations,the Ni_2P/Ni(OH)_2 heterojunction evolved from Ni_2P/FeP is identified as thereal high active phase for HER. This study not only builds a near-commercialbifunctional electrocatalyst for overall water splitting, but also provides adeep insight for synergistic catalytic mechanism of Ni and Fe species.