A Unique NiOOH@FeOOH Heteroarchitecture for Enhanced Oxygen Evolution in Saline Water

Abstract

The development of highly efficient non‐precious metal electrocatalysts for the oxygen evolution reaction (OER) in low‐grade or saline water is currently of great importance for the large‐scale production of hydrogen. In this study, by using an electrochemical activation pretreatment, metal oxy(hydroxide) nanosheet structures derived from self‐supported nickel–iron phosphide and nitride nanoarrays grown on Ni foam are successfully fabricated for OER catalysis in saline water. It is demonstrated that the different NiOOH and NiOOH@FeOOH (NiOOH grown on FeOOH) structures are generated from nickel–iron nitride and phosphide, respectively, after electrochemical activation. In particular, the NiOOH@FeOOH heteroarchitecture shows outstanding electrocatalytic performance with an ultralow overpotential of 292 mV to drive the current density of 500 mA cm−2. An unconventional dual‐sites mechanism (UDSM) is proposed to address the OER process on NiOOH@FeOOH and show that the FeOOH underlayer plays a critical role regarding the enhanced OER activity of NiOOH. The new possible UDSM involving two reaction sites presents a different understanding of the OER process on multi‐OH layer complexes, which is expected to guide the design of heteroarchitecture electrocatalysts.

MOF-Derived Iron–Cobalt Bimetallic Selenides for Water Electrolysis with High-Efficiency Oxygen Evolution Reaction

“…23,28,29 The peak at 505 cm −1 corresponds to the Co−O bond in Co−OOH, and the peak at 596 cm −1 corresponds to the shaking peaks of Co− O x . 30,43 The Raman analysis results are consistent with the XPS, suggesting the surface of Fe−CoSe PA is oxidized to Fe/ Co oxides of oxyhydroxides. The magnified transmission electron microscopy (TEM) image in Figure 4a clearly shows that the Fe-CoSe PA consists of many interconnected nanoparticles with a large number of pores distributed.…”

“…For Se 3d, the two peaks at 54.7 and 55.4 eV belong to Se 3d 5/2 and 3d 3/2 of Fe–CoSe PA, and can be assigned to the Se–metal bond. In addition, the peak at 59.4 eV is probably attributed to the Se-oxide species due to surface oxidation. ,,, Raman test was further carried out to probe the surface component of Fe–CoSe PA. As shown in Figure f, the distinct bands at 181.3, 190, and 256.4 cm –1 correspond to the Se–Se stretching modes of orthorhombic Fe–CoSe 2 . ,, The peak at 505 cm –1 corresponds to the Co–O bond in Co–OOH, and the peak at 596 cm –1 corresponds to the shaking peaks of Co–O x . , The Raman analysis results are consistent with the XPS, suggesting the surface of Fe–CoSe PA is oxidized to Fe/Co oxides of oxyhydroxides.…”

“…To probe the surface evolution of Fe–CoSe PA/CC under the OER test, in situ Raman analysis, shown in Figure a, is employed. Before the OER test, we can clearly observe the Raman signal of CoSe 2 at 250 and 173 and 688 cm –1 . , However, when voltage is applied, the two Raman peaks disappear, and two broad peaks centered at 516 and 695 cm –1 appear, which correspond to CoOOH species and FeOOH species, demonstrating that the surface of Fe–CoSe PA is oxidized to generate FeCoOOH species. , Therefore, the real catalytic site is the FeCoOOH; the inner Fe–CoSe serves as the conductive substrate for electron transfer. We noted that it has been frequently reported that CoFeOOH species are excellent OER catalysts. , XPS analysis is also performed on Fe–CoSe PA/CC after the stability test.…”

“…30,44 However, when voltage is applied, the two Raman peaks disappear, and two broad peaks centered at 516 and 695 cm −1 appear, which correspond to CoOOH species and FeOOH species, demonstrating that the surface of Fe−CoSe PA is oxidized to generate FeCoOOH species. 43,44 Therefore, the real catalytic site is the FeCoOOH; the inner Fe−CoSe serves as the conductive substrate for electron transfer. We noted that it has been frequently reported that CoFeOOH species are excellent OER catalysts.…”

Three-Dimensional Strawlike MoSe2-Ni(Fe)Se Electrocatalysts for Overall Water Splitting

“…Figure a shows the Raman spectrum of the sample post-OER with different testing times. When compared with that before OER, the Raman spectrum of MoSe 2 -NiFeSe post-OER with 5 h shows NiOOH peaks at 471 and 553 cm –1 , indicating the formation of NiOOH, i.e., partial Ni 2+ has been oxidized into Ni 3+ . , For a 15 h OER test, the intensity of the NiOOH peak becomes larger and is merged at the position of 535 cm –1 , meaning that more NiOOH is formed; meanwhile, the weak peak of FeOOH at the position of 696 cm –1 and the phonon mode of Mo–O at the position of 819 cm –1 are also found. − After a 48 h test, the signal-to-noise level for the Raman spectrum is too low to support fitting to detect effective phonon modes. Then, the valence state changes of each element after the OER test were analyzed by the XPS spectrum.…”