Non‐Noble‐Metal‐Based Electrocatalysts toward the Oxygen Evolution Reaction

The roles of oxygen vacancies in electrocatalytic oxygen evolution reaction

The modulation of electron density is an effective option for efficient alternative electrocatalysts. Here, p-n junctions are constructed in 3D free-standing FeNi-LDH/CoP/carbon cloth (CC) electrode (LDH=layered double hydroxide). The positively charged FeNi-LDH in the space-charge region can significantly boost oxygen evolution reaction. Therefore, the j at 1.485 V (vs. RHE) of FeNi-LDH/CoP/CC achieves ca. 10-fold and ca. 100-fold increases compared to those of FeNi-LDH/CC and CoP/CC, respectively. Density functional theory calculation reveals OH- has a stronger trend to adsorb on the surface of FeNi-LDH side in the p-n junction compared to individual FeNi-LDH further verifying the synergistic effect in the p-n junction. Additionally, it represents excellent activity toward water splitting. The utilization of heterojunctions would open up an entirely new possibility to purposefully regulate the electronic structure of active sites and promote their catalytic activities.

Utilizing the Space-Charge Region of the FeNi-LDH/CoP p-n Junction to Promote Performance in Oxygen Evolution Electrocatalysis.

The development of cost-effective catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is crucial for enhancing the energy efficiency of many electrochemical energy conversion and storage devices. Owing to their low cost and high activity, transition metal oxides have attracted much attention as alternative electrocatalysts to replace the currently used noble metal-based catalysts. Anion defects (e.g., oxygen vacancies, interstitials, and anion dopants) can significantly change the electronic structure of oxides or the stability of adsorbed intermediates, thus greatly enhancing the electrocatalytic activities of the oxide surface. Anionic defect engineering represents a potential new direction for rational design of high-performance electrocatalysts. In this review, recent progress in manipulating the anion defects in transition metal oxides for enhancing their activity and stability is summarized and the proposed mechanisms for enhanced performance are discussed in detail. Challenges and prospects are also discussed in the development of a new generation of highly efficient ORR and OER electrocatalysts.

Anionic defect engineering of transition metal oxides for oxygen reduction and evolution reactions

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial reactions in energy conversion and storage systems including fuel cells, metal–air batteries, and electrolyzers. Developing low-cost, highefficiency, and durable non-noble bifunctional oxygen electrocatalysts is the key to the commercialization of these devices. Here, based on an in-depth understanding of ORR/OER reaction mechanisms, recent advances in the development of non-noble electrocatalysts for ORR/OER are reviewed. In particular, rational design for enhancing the activity and stability and scalable synthesis toward the large-scale production of bifunctional electrocatalysts are highlighted. Prospects and future challenges in the field of oxygen electrocatalysis are presented.

Recent Advances in Non‐Noble Bifunctional Oxygen Electrocatalysts toward Large‐Scale Production

A Facile Strategy to Construct Amorphous Spinel-Based Electrocatalysts with Massive Oxygen Vacancies Using Ionic Liquid Dopant

Boosting oxygen evolution by surface nitrogen doping and oxygen vacancies in hierarchical NiCo/NiCoP hybrid nanocomposite

Constructing composite structures is an essential approach for obtaining multiple functionalities in a single entity. Available synthesis methods of the composites need to be urgently exploited; especially in situ construction. Here, a NiS/NiFe2O4 composite through a local metal−S coordination at the interface is reported, which is derived from phase reconstruction in the highly defective matrix. X‐ray absorption fine structure confirms that long‐range order is broken via the local metal−S coordination and, by using electron energy loss spectroscopy, the introduction of NiS/NiFe2O4 interfaces during the irradiation of plasma energy is identified. Density functional theory (DFT) calculations reveal that in situ phase reconfiguration is crucial for synergistically reducing energetic barriers and accelerating reaction kinetics toward catalyzing the oxygen evolution reaction (OER). As a result; it leads to an overpotential of 230 mV @10 mA cm−2 for the OER and a half‐wave potential of 0.81 V for the oxygen reduction reaction (ORR); as well as an excellent zinc−air battery (ZAB) performance with a power density of 148.5 mW cm−2. This work provides a new compositing strategy in terms of fast phase reconstruction of bifunctional catalysts.

Phase‐Reconfiguration‐Induced NiS/NiFe2O4 Composite for Performance‐Enhanced Zinc−Air Batteries

Boosting electrocatalysis by heteroatom doping and oxygen vacancies in hierarchical Ni-Co based nitride phosphide hybrid

Integration of amorphous structures and anion defects into ultrathin 2D materials has been identified as an effective strategy for boosting the electrocatalytic performance. However, the in-depth understanding of the relationship among the amorphous structure, vacancy defect, and catalytic activity is still obscure. Herein, a facile strategy was proposed to prepare ultrathin and amorphous Mo-FeS nanosheets (NSs) with abundant sulfur defects. Benefited from the ultrathin, amorphous nanostructure, and synergy effect of Mo-doping and sulfur defect, the Mo-FeS NSs manifested excellent electrocatalytic activity toward oxygen evolution reaction (OER) in alkaline medium, as shown by an ultralow overpotential of 210 mV at 10 mA cm-2, a Tafel slope of 50 mV dec-1, and retaining such good catalytic stability over 30 h. The efficient catalytic performance for Mo-FeS NSs is superior to the commercial IrO2 and most reported top-performing electrocatalysts. Density functional theory calculations revealed that the accelerated electron/mass transfer over the oxygen-containing intermediates can be attributed to the amorphous structure and sulfur-rich defects caused by structural reconfiguration. Furthermore, the S vacancies could enhance the activity of its neighboring Fe-active sites, which was also beneficial to their OER kinetics. This work integrated both amorphous structures and sulfur vacancies into ultrathin 2D NSs and further systematically evaluated the OER performance, providing new insights for the design of amorphous-layered electrocatalysts.

Zhiyu Shao

Papers

A Facile Strategy to Construct Amorphous Spinel-Based Electrocatalysts with Massive Oxygen Vacancies Using Ionic Liquid Dopant

Boosting oxygen evolution by surface nitrogen doping and oxygen vacancies in hierarchical NiCo/NiCoP hybrid nanocomposite

Phase‐Reconfiguration‐Induced NiS/NiFe2O4 Composite for Performance‐Enhanced Zinc−Air Batteries

Boosting electrocatalysis by heteroatom doping and oxygen vacancies in hierarchical Ni-Co based nitride phosphide hybrid

Engineering of Amorphous Structures and Sulfur Defects into Ultrathin FeS Nanosheets to Achieve Superior Electrocatalytic Alkaline Oxygen Evolution.