Interface engineering of three-phase nickel-cobalt sulfide/nickel phosphide/iron phosphide heterostructure for enhanced water splitting and urea electrolysis.

Rational designing efficient transition metal-based multifunctional electrocatalysts is highly desirable for improving the efficiency of hydrogen production from water cracking. Herein, a self-supported three-phase heterostructure electrocatalyst of nickel-cobalt sulfide/nickel phosphide/iron phosphide (CoNi5 S8 -Ni2 P-FeP2 ) was prepared by a two-step gas-phase sulfurization/phosphorization strategy. The heterostructure in CoNi5 S8 -Ni2 P-FeP2 provides a favorable interfacial environment for electron transfer and synergistic interaction of multiphase active components, while the introduced electronegative P/S not only serves as a carrier for proton capture in the hydrogen evolution reaction (HER) process but also promotes the metal-electron outflow, which in turn accelerates the generation of high-valent Ni3+ species to enhance the catalytic activity of oxygen evolution reaction (OER) and urea oxidation reaction (UOR). As expected, CoNi5 S8 -Ni2 P-FeP2 reveals excellent multifunctional electrocatalytic properties. An overpotential of 35/215 mV is required to reach 10 mA cm-2 for HER/OER. More encouragingly, a current of 100 mA cm-2 requires only 1.36 V for UOR with CoNi5 S8 -Ni2 P-FeP2 as anode, which is much lower as compared to the OER (1.50 V). Besides, a two-electrode water/urea electrolyzer assembled based on CoNi5 S8 -Ni2 P-FeP2 has a voltage of only 1.59/1.48 V when the system reaches 50 mA cm-2 . This work provides a new idea for the design of energy-efficient water/urea-assisted water-splitting multifunctional catalysts with multi-component heterostructure synergistic interface engineering.