Remarkable Bifunctional Oxygen and Hydrogen Evolution Electrocatalytic Activities with Trace-Level Fe Doping in Ni- and Co-Layered Double Hydroxides for Overall Water-Splitting

Abstract

Large-scale H2 production from water by electrochemical water-splitting is mainly limited by the sluggish kinetics of the nonprecious-based anode catalysts for oxygen evolution reaction (OER). Here, we report layer-by-layer in situ growth of low-level Fe-doped Ni-layered double hydroxide (Ni1–x Fe x -LDH) and Co-layered double hydroxide (Co1–x Fe x -LDH), respectively, with three-dimensional microflower and one-dimensional nanopaddy-like morphologies on Ni foam, by a one-step eco-friendly hydrothermal route. In this work, an interesting finding is that both Ni1–x Fe x -LDH and Co1–x Fe x -LDH materials are very active and efficient for OER as well as hydrogen evolution reaction (HER) catalytic activities in alkaline medium. The electrochemical studies demonstrate that Co1–x Fe x -LDH material exhibits very low OER and HER overpotentials of 249 and 273 mV, respectively, at a high current density of 50 mA cm–2, whereas Ni1–x Fe x -LDH exhibits 297 and 319 mV. To study the overall water-splitting performance using these electrocatalysts as anode and cathode, three types of alkaline electrolyzers are fabricated, namely, Co1–x Fe x -LDH­(+)∥Co1–x Fe x -LDH­(−), Ni1–x Fe x -LDH­(+)∥Ni1–x Fe x -LDH­(−), and Co1–x Fe x -LDH­(+)∥Ni1–x Fe x -LDH­(−). These electrolyzers require only a cell potential (E cell) of 1.60, 1.60, and 1.59 V, respectively, to drive the benchmark current density of 10 mA cm–2. Another interesting finding is that their catalytic activities are enhanced after stability tests. Systematic analyses are carried out on both electrodes after all electrocatalytic activity studies. The developed three types of electrolyzers to produce H2, are very efficient, cost-effective, and offer no complications in synthesis of materials and fabrication of electrolyzers, which can greatly enable the realization of clean renewable energy infrastructure.

Controlled Growth of LDH Films with Enhanced Photocatalytic Activity in a Mixed Wastewater Treatment

“…The chemical state of Fe ions in the LDH films was investigated by XPS spectra. The peaks at 726.28 and 712.78 eV are attributed to the 2p1/2 and 2p3/2 spin states of Fe(III) for LDH lamellar structure [28,29,30,31,32] as seen in Figure 1a. After Fe ion doping, the positions of Fe 2p3/2 were basically the same (within the experimental uncertainty [33]), while the peaks for Fe 2p1/2 in both LDH films showed a negative shift of ~0.4 and 0.6 eV, as shown in Figure 1b,c.…”

Alkaline Water Splitting Enhancement by MOF‐Derived Fe–Co–Oxide/Co@NC‐mNS Heterostructure: Boosting OER and HER through Defect Engineering and In Situ Oxidation

“…[67] In addition, the electrochemical impedance spectroscopy (EIS) measurement during HER demonstrated a smaller semicircular region for the mesoporous nanosheets of Fe-Co-O/Co@NC-mNS/NF, indicating its lower charge transfer resistance (R ct ) compared to that of the bulky Fe-Co-O/Co@NC/NF micropillar arrays, as shown in Figure S10 (Supporting Information). In principle, an ideal HER electrocatalyst is assumed to follow the Brønsted-Evans-Polanyi principle, and OH − adsorption affinity of the oxophilic groups should be optimum; that is, it should be neither x Fe x -LDH/NF, [62] Cu 0.3 Co 2.7 P/NC, [63] CoO x @CN, [7] Ni 1−x Fe x -LDH/NF, [62] and NiFe, [64] C) Tafel plots, and D) long-term chronopotentiometry stability test for Fe-Co-O/ Co@NC-mNS/NF electrocatalysts at the current density of 10 mA cm −2 for 50 h.…”

Addressing the sensitivity of signals from solid/liquid ambient pressure XPS (APXPS) measurement

“…The research interests of physicists, chemists and materials scientists have shifted significantly from the study of bulk properties of materials to the system behaviors at the interfaces. 1 The interactions and exchange of ions and electrons occurring at the solid/liquid interface are ubiquitous scenarios in electrocatalytic systems, e.g., CO 2 reduction [2][3][4] , hydrogen evolution reaction [5][6][7][8][9] , oxygen evolution reaction [10][11][12][13][14][15] , oxygen reduction reaction 16,17 , nitrogen fixation 18,19 etc., corrosion, as well as in energy storage systems, eg. lithium ion battery 20,21 .…”