Hierarchical Heterogeneous NiFe Layered Double Hydroxides for Efficient Solar-Powered Water Oxidation
Deok Ki Cho, Bingyi Yan, So Jeong Park, Young Seon Yoon, Hyun Woo Lim, Sun Kyung Hwang, Ik Jae Park, Jin Young Kim
Abstract
Highly active, stable, and low-cost oxygen evolution reaction (OER) electrocatalysts are urgently needed for the realization of large-scale industrial hydrogen production via water electrolysis. Layered double hydroxides (LDHs) stand out as one of the most promising nonprecious electrocatalysts worth pursuing. Here, a hierarchical heterogeneous Ni 2+ Fe 3+ @Ni 2+ Fe 2+ LDH was successfully synthesized via a sequential electrodeposition technique using separate electrolytes containing iron precursors with different valence states (Fe 2+, Fe 3+ ). The underlying highly crystalline Ni 2+ Fe 2+ LDH nanosheet array provides a large surface for the catalytically more active Ni 2+ Fe 3+ LDH overlayer with low crystallinity. The resulting Ni 2+ Fe 3+ @Ni 2+ Fe 2+ LDH demonstrates excellent OER activity with overpotentials of 218 and 265 mV to reach current densities of 10 and 100 mA cm –2, respectively, as well as good long-term stability for 30 h even at a high current density of 500 mA cm –2 . In an overall water splitting, an electrolyzer using an electrocatalyst of Sn 4 P 3 /CoP 2 as a cathode requires only a cell voltage of 1.55 V at 10 mA cm –2 . Furthermore, the solar-powered overall water splitting system consisting of our electrolyzer and a perovskite/Si tandem solar cell exhibits a high solar-to-hydrogen conversion efficiency of 15.3%.