Tuning Dynamically Formed Active Phases and Catalytic Mechanisms of In Situ Electrochemically Activated Layered Double Hydroxide for Oxygen Evolution Reaction

Abstract

The active phase and catalytic mechanisms of Ni-based layered double hydroxide (LDH) materials for oxygen evolution reaction (OER) have no common consensus and remain controversial. Moreover, engineering the site activity and the number of active sites of LDHs is an efficient approach to advance the OER activity, as the thickness and stacking structure of the LDHs layer limit the catalytic activity. This work presents an interesting in situ approach of tuning the site activity and number of active sites of NiMn-LDHs, which exhibit the superior OER performance (onset overpotential of 0.17 V and overpotential of 0.24 V at 10 mA cm–2). The fundamental mechanistic insights and active phases during the OER process are characterized by in operando techniques along with the computational density functional theory calculations, revealing that the Ni site constitutes the OER activity and the dynamically generated NiOOH moiety is the active phase. We also prove that Ni sites undergo a reversible oxidation state under the working conditions to create active NiOOH species which catalyze the water to generate oxygen. These findings suggest that the Ni­(III) phase in NiMn-LDHs is the OER active site and Mn promotes the electronic properties of Ni sites. Utilizing in situ/in operando techniques and theoretical calculation, we find that the in situ intercalation of guest anions allows the expansion of the LDH layers and keeps the active NiOOH species under the oxidation state of +3 via electron coupling, which ultimately tunes the site populations and site activity toward the superior OER activity, respectively. This work thus targets to provide insight into strategies to design the next generation of highly active catalysts for water electrolysis and fuel cell technologies.

Metal-Organic Frameworks Offering Tunable Binary Active Sites toward Highly Efficient Urea Oxidation Electrolysis

“…This implies that the Ni and Mn sites should synergistically work for the UOR process. The electrochemically active surface area (ECSA) is determined from the electrochemical double-layer capacitance (C dl ) [40]. As shown in Figure S12 and Figure 3(b), the NiMn 0.14 -BDC possesses the largest C dl value of 2.76 mF cm -2 , which is higher than those of the Ni-BDC (0.85 mF cm -2 ), NiMn 0.12 -BDC (0.86 mF cm -2 ), NiMn 0.13 -BDC (1.60 mF cm -2 ), NiMn 0.16 -BDC (1.94 mF cm -2 ), and NiMn 0.19 -BDC (1.78 mF cm -2 ), suggesting that more active sites are exposed in NiMn 0.14 -BDC.…”

Co-N-Doped Directional Multichannel PAN/CA-Based Electrospun Carbon Nanofibers as High-Efficiency Bifunctional Oxygen Electrocatalysts for Zn–Air Batteries

“…The parameters of Co-N@PCNFs-0.2 actually exceed those of most of the non-noble metal-based catalysts reported in the previous literature (Table S3). Furthermore, the Tafel slope of Co-N@PCNFs-0.2 (76 mV dec –1 ) is also less than that of the commercial 20 wt % Pt/C (78 mV dec –1 ), which further proves the excellent ORR reactive kinetics of Co-N@PCNFs-0.2 (Figure d). , …”

“…Furthermore, the Tafel slope of Co-N@PCNFs-0.2 (76 mV dec −1 ) is also less than that of the commercial 20 wt % Pt/C (78 mV dec −1 ), which further proves the excellent ORR reactive kinetics of Co-N@PCNFs-0.2 (Figure 5d). 7,11 We conducted the CV test at different RDE rotation rates (225−2025 rpm) to further evaluate the ORR diffusion kinetics of the catalyst (Figure 5e). The K−L plot (the inset of Figure 5e) drawn from the LSV curves shows a good linear relationship and a similar slope.…”

“…With the demand for green/sustainable development, the research and development of efficient, sustainable, and clean energy sources have become more and more urgent worldwide. − Zn–air batteries have become competitive battery candidates for portable energy storage devices because of high safety, low production cost, large capacity, and stable discharge curves. − However, the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at the air electrode of Zn–air batteries exhibit apparent disadvantages such as slow kinetics and high overpotentials, which greatly hinder the commercialization of Zn–air batteries. − Although Pt, Ru, or Ir-based noble catalysts have extremely high catalytic performance, the disadvantages of scarcity and durability severely limit their large-scale use. , Correspondingly, nonprecious metal electrocatalysts with merits of a wide range of sources and low cost have received widespread attention. Therefore, the effective and rational construction of nonprecious metal bifunctional oxygen catalysts presents high research prospects and commercial values. − …”

Evaluating Properties of Carbon-Free Nano-NiCoFe-LDHs with Molybdate as Oxygen Evolution Catalysts and Their Applications in Rechargeable Air Electrodes

“…7 It has been verified that the OER activity of LDHs can be significantly boosted by the strategy of engineering nanostructures, such as reducing the size and thickness of LDH sheets to expose more active sites. 7,15,16 Another important strategy to promote OER catalytic activities is to design multi-metal LDHs. In comparison to the binary LDHs, the trimetallic LDHs can generate more quantities of catalytic active sites and show significant improvement for OER activities.…”