Valence‐State Effect of Iridium Dopant in NiFe(OH)₂ Catalyst for Hydrogen Evolution Reaction

Abstract

Engineering high‐performance electrocatalysts is of great importance for energy conversion and storage. As an efficient strategy, element doping has long been adopted to improve catalytic activity, however, it has not been clarified how the valence state of dopant affects the catalytic mechanism and properties. Herein, it is reported that the valence state of a doping element plays a crucial role in improving catalytic performance. Specifically, in the case of iridium doped nickel‐iron layer double hydroxide (NiFe‐LDH), trivalent iridium ions (Ir3+) can boost hydrogen evolution reaction (HER) more efficiently than tetravalent iridium (Ir4+) ions. Ir3+‐doped NiFe‐LDH delivers an ultralow overpotential (19 mV @ 10 mA cm−2) for HER, which is superior to Ir4+ doped NiFe‐LDH (44 mV@10 mA cm−2) and even commercial Pt/C catalyst (40 mV@ 10 mA cm−2), and reaches the highest level ever reported for NiFe‐LDH‐based catalysts. Theoretical and experimental analyses reveal that Ir3+ ions donate more electrons to their neighboring O atoms than Ir4+ ions, which facilitates the water dissociation and hydrogen desorption, eventually boosting HER. The same valence‐state effect is found for Ru and Pt dopants in NiFe‐LDH, implying that chemical valence state should be considered as a common factor in modulating catalytic performance.

Constructing a Hetero-interface Composed of Oxygen Vacancy-Enriched Co3O4 and Crystalline–Amorphous NiFe-LDH for Oxygen Evolution Reaction

“…The peaks of Raman shift in NiFe-60/Co 3 O 4 @NF at 474 and 539 cm –1 correspond to Ni 2+ –O–Ni 2+ /Fe 3+ and Fe 3+ –O–Fe 3+ , respectively, while another peak at 689 cm –1 is attributed to the intercalated CO 3 2– , reflecting the formation of NiFe-LDH. For NiFe-60@NF, the same bands corresponding to the above functional groups appear at around 462, 546, and 678 cm –1 , respectively. − Obviously, the red shift or blue shift was presented according to the comparison of these peaks (NiFe-60/Co 3 O 4 @NF vs NiFe-60@NF: 474 vs 462 cm –1 , 539 vs 546 cm –1 , 689 vs 678 cm –1 ). They should be ascribed to the lattice distortion caused by the increased defects that originated from the formation of the amorphous phase in NiFe-LDH .…”

Engineering Different Reaction Centers on Hierarchical Ni/NiFe Layered Double Hydroxide Accelerating Overall Water Splitting

“…This accounts for the higher HER activity of Ni/NiFe LDH, comparing with E-Ni and NiFe LDH. As for OER, the additional nickel can reduce the electron transport resistance, and there are many previous works and DFT calculations that prove the extremely excellent OER catalytic activity. , Overall, the theoretical simulation reveals that the abundant heterostructure interfaces considerably improve the electronic conductivity and reduce reaction barriers, thus resulting in superior OWS activity.…”

“…The interface between E-Ni and NiFe LDH is built by Ni (111) and NiFe LDH (001) (Figures S26, S27) because of a small interfacial lattice mismatch, which is a common approach in constructing a heterostructure for theoretical calculations. 48 The charge density difference of Ni/NiFe LDH was analyzed (Figure 5a,b 58,59 Overall, the theoretical simulation reveals that the abundant heterostructure interfaces considerably improve the electronic conductivity and reduce reaction barriers, thus resulting in superior OWS activity. 2.5.…”

Single atoms (Pt, Ir and Rh) anchored on activated NiCo LDH for alkaline hydrogen evolution reaction

“…2c shows the Pt 4f spectrum of Pt/A-NiCo LDH, where the peaks located at 72.72 and 76.1 eV are ascribed to the Pt 2+ 4f 7/2 and Pt 4f 5/2 , respectively. In addition, the Ir 4f and Rh 3d spectra confirm the existence of Ir 3+ and Rh 3+ , respectively 14,15 (Fig. S14, ESI†).…”

“…1–3 At present, noble metals ( e.g. Pt, 4 Pd, 5 Ir 6 and Ru) are considered as the benchmark electrocatalysts for the HER in acid and alkaline conditions, respectively. However, the high cost, limited resources and poor stability largely hinder their large-scale application.…”