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span1 span1 _span1 author 1span span1 _span1 _span1 _span1 The first author: . Sharp, Li Yanbo
Communication unit: Technical University of Munich, University of Electronic Science and Technology
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strong 51strong Full text quick overview
However, this strategy is still a challenge for OER catalysts that work under high alkaline conditions. Due to the irreversible leaching of Fe catalytic centers, the self-repair technology of OER active nickel-iron layered double hydroxide (NiFe-LDH) has not yet been realized.Here, the author studied the introduction of cobalt (Co) into NiFe-LDH as an accelerator for in-situ iron redeposition. The author synthesized an active borate intercalation NiCoFe-LDH catalyst by electrodeposition. It did not degrade after 10 mA cm -2 , pH 14, OER test for 1000 h, which proved that it was under OER conditions With self-healing ability. Importantly, the authors found that the presence of ferrous ions and borate ions in the electrolyte is critical to the self-repair of the catalyst. In addition, the catalyst realizes the application in the photoelectrochemical device through the integrated silicon photoanode. The self-repair mechanism results in a self-limiting catalyst thickness, which is ideal for integration with photoelectrodes, because redeposition will not be accompanied by increased light absorption.
background introduction
is the key way to transform solar energy and wind energy into sustainable energy storage in the future. At present, the two main ways that are being studied in depth are electrocatalytic water splitting and carbon dioxide (CO 2 ) reduction. The hydrogen and hydrocarbons produced through these processes can be used as long-term storage energy carriers, providing renewable transportation fuels, and realizing multifunctional power generation and distribution. Although these high value-added chemicals are produced by the reduction reaction of water or CO 2 at the cathode,However, the anode hydroxyl ion oxidation is required to provide a rich source of electrons and protons and complete the entire reaction. Therefore, as researchers seek for hydrogen evolution reaction (HER) and CO 2 reduction reaction (CO 2 RR) high performance catalyst with challenging oxygen evolution kinetics, Reaction (OER) The development of efficient and durable catalysts is equally important.
In the past ten years, the activity of OER catalysts in this field has been significantly improved. Among these active OER catalysts, nickel-iron layered double hydroxide (NiFe-LDH) has become one of the most promising candidates due to its rich earth composition and high OER activity under alkaline conditions. Although there is controversy regarding the role of Fe as an active center or as a Lewis acid that enhances Ni activity, it is generally accepted that Fe promotes the OER activity of Ni oxyhydroxide. Recent mechanism studies strongly indicate that iron constitutes the active center of OER in NiFe-LDH, and nickel hydroxide lattice provides a stable body of thermodynamics to accommodate the catalytic Fe center. However, it has been found that high-valence active Fe intermediates are thermodynamically unstable under OER conditions. These catalytic Fe centers may be leached from the catalyst during the reaction, which will cause the OER activity to decrease over time. In order to achieve the final stability of the catalyst, some people think that the self-repair of the leaching catalytic center may be the only effective strategy. Although NiFe oxyhydroxide,The energy-regulated surface adsorption of Fe from the electrolyte proved the short-term (1 h) dynamic stability of Fe active centers, but for NiFe-LDH catalysts, long-term effective self-repair strategies have not yet been achieved. Therefore, the long-term stability of these catalysts represents a critical performance gap that must be overcome to achieve a practical system containing this outstanding OER catalyst.
Graphic analysis
img2 p0 p0 catalyst failure. a NiFe-B i catalyst stability test, at 10 mA cm -2 _span3 span1 span_span3 span_span1 span_span1 span_span3 span_span3 span_span3 electrolyte at a constant current density of span_span3 span_span1 span_span1 span_span1 100 hours, containing 50 μM Fe(II) ions. b NiFe-B i OER polarization curve of the catalyst before and after the stability test. The curve is measured at a scan rate of 1 mV s -1 ,There is no iR correction. c In the iron-containing KB i electrolyte, the iron hydroxide deposition rate on the EQCM sensor under different potential . The gap between the blue and green regions illustrates the mismatch between the OER operating potential and the potential required for effective iron redeposition. d The mechanism of self-repair failure of iron-based catalysts. OER catalysis is simplified by considering FeO 4 2- as a representative active intermediate that is thermodynamically unstable and may be leached from the catalyst.
Figure 2. NiCoFe-B i _span3 catalyst. a Schematic diagram of the structure of NiCoFe-Bi catalyst. The basal layer is composed of a mixture of [FeO 6 ], [CoO 6 ] and [NiO _span 1 span 1 span] and [NiO 3 span 1 span]And insert [B 4 O 5 (OH) 4 ] 2- ions. b In-situ deposition of metal oxyhydroxide on the FTO substrate. Add 50 μM Ni(II), Fe(II), and Co(II) ions in sequence to the KB i electrolyte at pH 14. After adding each ion, perform 20 cyclic voltammetry (CV) scans between 1.01 and 1.71 V vs. RHE at a scan rate of 50 mV s −1 . c at constant current density of 10 mA cm -2 in i pH KB 14 of the catalyst thin film i electrolyte successively measured three NiCoFe-B Chronopotentiometric curve.d Compare the stability of NiCoFe-B i catalyst in KB i electrolyte with and without Fe(II) ions. e NiCoFe-B catalyst measured in KB i electrolyte when 30 μM Ni(II), Co(II) or Fe(II) ions are added after 0.5 h. The chronopotential curve of the film, pH is 14. f Co-catalyzed self-repair mechanism of the proposed NiCoFe-B i catalyst.
Figure 3. NiCoFe-B deposited on FTO substrate i self-healing and intrinsic performance of catalyst span a NiCoFe-B i The OER polarization curve of the catalyst before and after 100 h of stability test in different electrolytes.The curve is measured at a scan rate of 1 mV s -1 without iR correction. b 100 h chronopotential curve of the NiCoFe-B i catalyst measured at a constant current density of 10 mA cm −2 in different electrolytes. c Quantitative ICP-MS analysis of NiCoFe-B i catalyst before and after 100 h stability test in different electrolytes. d NiCoFe-B i Catalyst for oxygen evolution TOF in different electrolytes. These values are calculated using polarization curves and ICP-MS data measured after a 100-hour stability test. e Tafel diagrams of NiCoFe-B i catalysts in different electrolytes. f NiCoFe-B i The mass activity of the catalyst is compared with the reported value.
Figure 4. NiCoFe-B i The catalyst's self-healing ability was tested under various conditions.NiCoFe-B i The chronopotentiometric test of the catalyst (a) on the FTO substrate, at 10 mA cm −2 span_span span_span_span3 span_span_span_span_span_span_span_span_span_span_span_span_span_span_span_span_span_span_span_span_span_span_span_span_span_span_span1 (B) On the Au substrate, at 100 mA cm −2 , at pH 14 KB i i for 200 hours, and electrolyte On Au substrate, in 300 mA cm -2 , at pH 14.9 KB i electrolyte for 100 hours. The polarization curves before and after the stability test are plotted in (d-f). All polarization curves are measured at a scan rate of 1 mV s -1 ,All potentials are not corrected for iR loss.
Figure 5. Integrated NiCoFe-Bi/NiO/CuO x /PE span3span/PE performance of the photoelectric anode. a Schematic diagram of the PEC device. b 100 h photoanode chrono current curve measured at 1.2 V vs. RHE at AM 1.5 G. c J-V curve of photoanode before and after stability test in AM 1.5 G and darkness. d ABPE curve of the photoanode before and after the stability test.
Summary and outlook
is based on the above-mentioned result of the Fe-H FeH-based self-repair strategy. The long-term stability of the catalyst is a problem. In the usual configuration, the self-healing of NiFe-LDH catalyst is impossible because the catalytic Fe cannot be redeposited at the OER operating potential. The author proposed and studied the introduction of Co as a promoter of Fe in-situ redeposition. The author used a simple electrodeposition method to synthesize a highly active borate intercalation NiCoFe-LDH catalyst at 10 mA cm −2 ,It can last for 1000 h at pH 14 (at 300 mA cm −2 , after 100 h of OER test at pH 14.9, there is no sign of degradation), proving that it has extraordinary self-repair under severe OER conditions ability. The self-healing NiCoFe-B i catalyst realized by the author for OER under high alkaline conditions can not only find applications in commercial alkaline water electrolyzers, but also in the most advanced CO 2 RR electrocatalytic system found application. In addition, it is also suitable for integration into PEC systems. More importantly, the mechanism proposed in this paper provides new guidance for the development of self-repairing catalysts by using other components specifically designed to promote the self-repair of the catalytic center.
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