Search

The development of electrocatalysts for the oxygen evolution reaction (OER) especially in acidic media remains the major challenge that still requires significant advances, both in material design and mechanistic exploration. In this study, the incorporation of cobalt in Y2‐xCoxRu2O7−δ results in an ultrahigh OER activity because of the charge redistribution at eg orbitals between Ru and Co atoms. The Y1.75Co0.25Ru2O7−δ electrocatalyst exhibits an extremely small overpotential of 275 mV in 0.5 m H2SO4 at the current density of 10 mA cm−2, which is smaller than that of parent Y2Ru2O7−δ (360 mV) and commercial RuO2 (286 mV) catalysts. The systematic investigation of the composition related to OER activity shows that the Co substitution will also bring other effective changes, such as reducing the bandgap, and creating oxygen vacancies, which result in fast OER charge transfer. Meanwhile, the strengthening of the bond hybridization between the d orbitals of metal (Y and Ru) and the 2p orbitals of O will intrinsically enhance the chemical stability. Finally, theoretical calculations indicate that cobalt substitution reduces the theoretical overpotential both through an adsorbate evolution mechanism and a lattice oxygen‐mediated mechanism. [ABSTRACT FROM AUTHOR]

High-valence metals (such as, Mo, W, Zr and Nb) have recently been reported that promote oxygen evolution reaction (OER) activity of the 3 d -transition metal electrocatalysts. These high-valence metals play a key role on surface self-reconstruction process and stabilizing the low-valence active sites. However, further understand their effect on the OER mechanism is challenging, especially in amorphous electrocatalysts with complicated structure. Here, we integrate high-valence Mo with 3 d metals (Fe, Co and Ni), fabricating Fe 34-x Co 25 Ni 25 Mo x P 8 B 8 amorphous electrocatalysts by the melt-spinning method. We employ in-situ Raman spectroscopy to characterize the species evolution during OER, and find that the higher OER performance is originated from a bifunctional mechanism involves two catalytic sites (NiOOH and FeOOH) enabled by high-valence Mo dissolution. Benefit from this, the Fe 34-x Co 25 Ni 25 Mo x P 8 B 8 with Mo show higher OER performance compared with Fe 34-x Co 25 Ni 25 Mo x P 8 B 8 without Mo. For 3d-metal OER electrocatalyst, this study provides a new understanding on the effect of high-valence metals. [ABSTRACT FROM AUTHOR]

• Demonstrating a dealloyed Ni-Fe-B-Si-P amorphous electrocatalyst. • Intrinsic activity plays a crucial role for OER performance in dealloyed ribbons. • Dealloying shortens the evolution path (Ni0 → Ni2+ → Ni3+ → Ni4+) toward Ni4+ species. • The oxidation and leaved of B, P, and Si promote the surface reconstruction in OER. Designing high-efficiency and freestanding electrocatalysts hold immense importance in addressing the limitations of powdered electrocatalysts and accelerating the sluggish kinetics of the oxygen evolution reaction (OER) in advancing energy technologies. While dealloyed amorphous ribbons have been shown to be active and self-supporting electrocatalysts toward OER, the underlying enhancement mechanism remains unclear. Here, we developed a dealloyed Ni-Fe-B-Si-P amorphous electrocatalysts with a mixed oxide layer (including oxo-anions: phosphate, silicate, and borate). The dealloyed oxide layer optimizes the surface properties and chemical local environment of the amorphous ribbon, then shortens the multistep evolution path (Ni0 → Ni2+ → Ni3+ → Ni4+) toward Ni4+ species during the surface reconstruction process and decreased energy barriers for the dealloyed Ni-Fe-B-Si-P electrocatalyst during OER. Benefiting from the changes, the dealloyed Ni-Fe-B-Si-P enables a 56-fold increase in current density (at overpotential: 320 mV) and an 8-fold increase in turnover frequency values compared to undealloyed Ni-Fe-B-Si-P, demonstrating the major effect of the intrinsic activity on the OER performance of the dealloyed ribbon. This work sheds light on the enhancement mechanism of amorphous bulk electrocatalysts and offers valuable insights into the rational design of amorphous components and surface treatment processes. [ABSTRACT FROM AUTHOR]

We found the nickel-based phosphides are actually acting as pre-electrocatalysts in OER, and also in battery reactions of rechargeable Zn-air batteries, which are well disclosed by detailed experimental and theoretical investigations. [Display omitted] Zinc-air batteries (ZnABs) with high theoretical capacity and environmental benignity are the most promising candidates for next-generation electronics. However, their large-scale applications are greatly hindered due to the lack of high-efficient and cost-effective electrocatalysts. Transition metal phosphides (TMPs) have been reported as promising electrocatalysts. Notably, (Ni 1 −x Cr x) 2 P (0 ≤ x ≤ 0.15) is an unstable electrocatalyst, which undergoes in-situ electrochemical oxidation during the initial oxygen evolution reaction (OER) and even in the activation cycles, and is eventually converted to Cr-NiOOH serving as the actual OER active sites with high efficiency. Density functional theory (DFT) simulations and experimental results elucidate that the OER performance could be significantly promoted by the synergistic effect of surface engineering and electronic modulations by Cr doping and in-situ phase transformation. The constructed rechargeable ZnABs could stably cycle for more than 208 h at 5 mA cm−2, while the voltage degradation is negligible. Furthermore, the developed catalytic materials could be assembled into flexible and all-solid-state ZnABs to power wearable electronics with high performance. [ABSTRACT FROM AUTHOR]

[Display omitted] Annealing and cyclic voltammetry (CV) are essential for the activation of amorphous alloy ribbons. Various amorphous alloy ribbons have been activated in the fields of environmental catalysts using either annealing or CV. However, the combination of the two methods for improving the oxygen evolution reaction (OER) performance has rarely been reported. This combination is expected to significantly improve the OER performance of amorphous ribbons. Here, we developed an "annealing +CV-activation" integrated strategy to treat a free-standing NiFeBSiP ribbon, which as an efficient and stable oxygen-evolving electrode. The "annealing +CV-activation" strategy induces the nanocrystallization and oxidation effects on the surface of the NiFeBSiP ribbon. The effects significantly increase the electron transfer ability, the Ni/Fe/P oxidation state and the surface area of the NiFeBSiP ribbon, which consequently leads to enhancing the OER performance. As a result, the treated ribbon exhibits a low overpotential of 269 mV at 10 mA cm−2 and a small Tafel slope of 40.5 mV dec−1, which are much better than the OER performance of the as-spun ribbon. The enhanced OER performance of the NiFeBSiP ribbon demonstrates the significant and promising effect of the "annealing +CV-activation" integrated strategy for designing high-efficiency amorphous alloy ribbons electrocatalysts. [ABSTRACT FROM AUTHOR]

Amorphous ribbons, as one class free-standing OER electrocatalyst, have been attracted attention. It is crucial that achieving the efficient and durable amorphous ribbon for oxygen evolution reaction (OER) by exploring suitable methods. Herein, it is reported that the self-supporting Fe 25 Co 25 Ni 25 Mo 9 P 8 B 8 amorphous ribbon is treated via dealloying or annealing method. The optimal dealloyed ribbon exhibits a low overpotential of 281 mV at 10 mA cm−2, the small Tafel slope of 36.49 mV dec−1 and excellent stability, which are obviously superior to those of the raw ribbon and the annealed ribbon. The fast self-reconstruction of active layer in amorphous structure and the protection effect of Mo/P oxide layer induced by dealloying significantly boost the OER activity and stability of the amorphous ribbon. This work provides a different angle on the exploring of reasonable method to optimize the amorphous ribbon electrocatalysts and facilitates the practical applications of ribbon electrocatalysts. [Display omitted] • The OER performance of the dealloyed ribbon is obviously superior to those of the raw ribbon andthe annealed ribbon. • The stable amorphous structure and higher Mo/P oxidation states are key for the OER performanceof the dealloyed ribbon. • In-situ Raman spectrum reveals that Fe oxyhydroxide is the active layer of the dealloyed ribbon. [ABSTRACT FROM AUTHOR]

Non-precious metals as oxygen evolution reaction (OER) electrocatalysts for water-splitting purposes has recently attracted extensive attention. However, alloy ribbons of non-precious metals as self-supported electrodes for OER electrocatalysts have rarely been reported. Here we report a melt-spinning method to prepare an Fe 35 Co 20 Ni 20 Mo 20 Si 5 alloy ribbon, which serves as a self-supporting electrode OER electrocatalysts by dealloyed etching. The etching expands the active surface area of the alloy ribbon which increases the abundant active sites. The experimental results showed that the electronic structure of FeMoSi on the ribbons surface excellently facilitates the OER process. The electrocatalytic activity test showed that the etched alloy ribbon exhibited excellent OER activity in 1 M KOH alkaline solution, with an overpotential of only 260 mV at a current density of 10 mA cm−2, a Tafel slope as low as 37.9 mV dec−1 and a stability of up to 90 h without decay. This work serves as a promising guide for the use of alloy ribbons as a highly efficient and self-supported electrocatalyst. Schematic illustration for the preparation of Fe 35 Co 20 Ni 20 Mo 20 Si 5 alloy ribbon, and the polarization curve of alloy ribbons. [Display omitted] • The Fe 35 Co 20 Ni 20 Mo 20 Si 5 -etched alloy ribbon as self-supported electrode for OER. • The Fe 35 Co 20 Ni 20 Mo 20 Si 5 -etched alloy ribbons deliver remarkable OER activity (η 10 = 260 mV）and robust stability up to 90 h without decay. (j = 10 mA cm−2). • It is revealed that a strong positive correlation exists among ECSA, electronic structure and OER activity. [ABSTRACT FROM AUTHOR]