Computational calculations and experimental studies reveal that the CoOOH phase and the intermediate-spin (IS) state are the key factors for realizing efficient Co-based electrocatalysts for the oxygen evolution reaction (OER). However, according to thermodynamics, general cobalt oxide converts to the CoO2 phase under OER condition, retarding the OER kinetics. Herein, we demonstrate a simple and scalable strategy to fabricate electrodes with maintaining Fe-CoOOH phase and an IS state under the OER. The changes of phase and spin states were uncovered by combining in-situ/operando X-ray based absorption spectroscopy and Raman spectroscopy. Electrochemical reconstruction of chalcogenide treated Co foam affords a highly enlarged active surface that conferred excellent catalytic activity and stability in a large-scale water electrolyzer. Our findings are meaningful in that the calculated results were experimentally verified through the operando analyses. It also proposes a new strategy for electrode fabrication and confirms the importance of real active phases and spin states under a particular reaction condition.

Evolving cost-effective transition metal phosphides (TMPs) using general approaches for energy storage is pivotal but challenging. Besides, the absence of noble metals and high electrocatalytic activity of TMPs allow their applicability as catalysts in oxygen evolution reaction (OER). Herein, CoNiP-CoP 2 (CNP-CP) composite is in situ deposited on carbon fabric by a one-step hydrothermal technique. The CNP-CP reveals hybrid nanoarchitecture (3D-on-1D HNA), i.e., cashew fruit-like nanostructures and nanocones. The CNP-CP HNA electrode delivers higher areal capacity (82.8 𝝁Ah cm -2 ) than the other electrodes. Furthermore, a hybrid cell assembled with CNP-CP HNA shows maximum energy and power densities of 31 𝝁Wh cm -2 and 10.9 mW cm -2 , respectively. Exclusively, the hybrid cell demonstrates remarkable durability over 30 000 cycles. In situ/operando X-ray absorption near-edge structure analysis confirms the reversible changes in valency of Co and Ni elements in CNP-CP material during real-time electrochemical reactions. Besides, a quasi-solid-state device unveils its practicability by powering electronic components. Meanwhile, the CNP-CP HNA verifies its higher OER activity than the other catalysts by revealing lower overpotential (230 mV). Also, it exhibits relatively small Tafel slope (38 mV dec -1 ) and stable OER activity over 24 h. This preparation strategy may initiate the design of advanced TMP-based materials for multifunctional applications.

Ammonia has recently received considerable attention as an alternative energy carrier and a carbon-neutral fuel. In this future energy scenario, the ammonia oxidation reaction (AOR) is a pivotal process for onsite hydrogen production and/or electricity generation. However, its implementation is hindered by the nondurable nature of AOR catalysis by platinum. Accordingly, securement of a durable Pt electrocatalysis for the AOR is critical but has been hampered by the well-known chemical deactivation (i.e., poisoning). Additionally, the structural stability, which could also affect durable AOR operation, has scarcely been investigated. Herein, the degradation of Pt catalysts under AOR conditions has been investigated with various operando and in/ex situ spectroscopies. We demonstrate that NH3 (or AOR intermediates/byproducts) modifies the chemical structures of both the Pt surface and dissolved Pt ions, specifically by passivation of the Pt surface with NH3-derived adsorbates and complexation of the dissolved Pt ions, respectively. These modifications lead to a significant acceleration in Pt dissolution but a deceleration in its redeposition, resulting in the augmented structural degradation of Pt catalysts in NH3-containing electrolyte after the Pt has experienced a potential excursion above ca. 1 VRHE. With these understandings, a quasi-stable operation potential window and operational strategy are suggested. The tentative AOR protocol allows prolonged NH3 electrolysis with alleviated Pt dissolution (<0.02 ng cmPt –2 s–1), suggesting that NH3 will be a viable future energy carrier if the rational operational strategy proposed herein is developed further.

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as a side reaction, thereby diminishing the selectivity of the CO 2 RR. To increase the selectivity and catalytic activity of the CO 2 RR, several materials, such as Ag, Cu, Au, Sn, N-coordinated Ni single atoms (NiNC), FeNC, and so on have been reported as electrochemical catalysts. [4][5][6][7][8][9][10][11][12] These catalysts possess high H* chemisorption energies and moderate *COOH chemisorption energies, suppressing the HER and accelerating formation of carbonaceous products. In contrast, other materials such as bulk Ni and Pt have low H* chemisorption energies, exhibiting small kinetic barrier and high selectivity for the HER. [2,13,14] Single-atom catalysts have attracted significant attention from researchers because their properties significantly differ from those of bulk materials. Many previous studies focused on determining efficient designs of single-atom catalysts to maximize their activity. [4,15,16] Generally, a NiNC catalyst has a structure in which a support N atoms surrounds the center of a single Ni atom, exhibiting outstanding catalytic activity, unlike bulk N-coordinated Ni single atom (Ni-NC) is one of the best catalysts for the CO 2 reduction reaction (CO 2 RR) to produce CO. However, no bulk Ni materials have exhibited high catalytic activity for CO 2 RR. Herein, it is shown that NiS nanoparticles mimicking the electronic structure of Ni-NC in real-time enhance the CO 2 RR activity in a zero-gap electrolyzer. In situ/Operando X-ray absorption spectroscopy suggests that under a cathodic potential, the electronic structure of NiS changes similarly to that of Ni-NC and modulated O x-z S y ligands with similar properties to Ni ligands, resulting in a mimicked electronic structure. However, NiS exhibits low stability owing to the loss of S species, key to mimicking N ligands. The future challenges in finding a stable mimicked electronic structure are discussed. Moreover, this work provides new insights into the development of catalysts from materials that have not generally been considered previously.

Sulfurized NiFeCo OER electrocatalysts for water splitting in alkaline conditions.

The demand for non-noble bifunctional electrocatalysts for overall water splitting was increased for simplifying water-splitting systems and accelerating commercialization. Herein, oxygen vacancy-rich nanoporous nickel foam (NF) electrodes decorated with nanosized NiFe layered double hydroxide are fabricated by a facile and scalable electrochemical treatment using FeCl3 solutions as OER and HER electrocatalysts in an alkaline medium. The roles of Cl– and Fe3+ ions are analyzed by electrochemical and surface-enhanced X-ray analysis techniques. The Cl anions increase the active sites by producing nanopores on the NF surface and promote oxygen vacancies, while the Fe cations enhance the inherent catalytic activity for water oxidation. The FeCl3-treated NF shows enhanced catalytic activities and maintains an overpotential of 520 mV at 100 mA cm–2 for 150 h in a 10 cm2 single cell. The results demonstrate that the simple electrochemical treatment is a promising method to produce oxygen vacancy-induced scalable electrodes with large surface areas for various applications.

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