Atomistic Investigation of Doping Effects on Electrocatalytic Properties of Cobalt Oxides for Water Oxidation

Low Pt Loading on Wolframite-Type NiWO4 to Excel the Electrocatalytic Water Splitting and Ammonia Oxidation Reaction

Hydrogen production via water-splitting or ammonia electrolysis using transition metal-based electrodes is one of the most cost-effective approaches. Herein, ca. 1-4% of Pt atoms are stuffed into a wolframite-type NiWO4 lattice to improve the electrocatalytic efficiency. The co-existence of atomically dilute quantities of Pt0 and PtIV atoms in the NiWO4 without altering the lattice structure is established via powder X-ray diffraction, inductively coupled plasma mass spectrometry (ICP-MS), core-level X-ray photoelectron spectroscopy, and other spectroscopic studies. While the undoped NiWO4 and a physical mixture of Pt0 (2 wt %) and NiWO4 exhibit poor oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and ammonia oxidation reaction (AOR) activities, 3-4% Pt-enriched NiWO4 depict improved electrocatalytic performances with at least 50 mV overpotential drop for both the OER and HER. The 3%Pt/NiWO4 electrode showcases a long-term (for 110 h) chronoamperometric/chronopotentiometric OER and HER performance, delivering high current at a low working potential. The bifunctional behavior of the material leads to the development of a water-splitting electrolyzer, 3%Pt/NiW/NF(-)/(+)3%Pt/NiW/NF, achieving >90% Faradaic efficiency for H2 production. The onset potential for the AOR is also cathodically shifted for 3%Pt/NiW and 4%Pt/NiW compared to the NiWO4 itself. Electrokinetic study through a rotating ring-disk electrode (RRDE) experiment and the Koutecký-Levich study provides an observed rate constant (kobs) of 1.68 × 10-3 cm s-1 of AOR with a 6e- count from the kinetic current region, highlighting [NO2]- as the major product. The electrolysis of 1 M NH3 using 4%Pt/NiW/NF as a working electrode produces predominantly [NO2]- (FE: 53%) and [NO3]- (FE: 30%). The improved electrocatalytic activity of 3-4% Pt-enriched NiWO4 can be due to the low Tafel slope and charge transfer resistance (Rct). Pt0 being electron-rich induces facile electronic conduction during electrocatalysis and enhances a better binding of the analytes such as H2O, [OH]-, and NH3. At the same time, the PtIV centers present adjacent to the NiII sites can polarize the electron density to stabilize NiIII species and enhance the possibility of OER and AOR. This study demonstrates the effect of hetero-metal doping to tune the electronic structure to improve the electrochemical activity. The low-Pt-doped NiWO4 material is presented here as a multimodal electrocatalyst that can efficiently electrolyze water or ammonia to produce hydrogen.

Design and Optimization of Nanoporous Materials as Catalysts for Oxygen Evolution Reaction-A Review

With the growing demand for new energy sources, electrochemical water splitting for hydrogen production is a technology that must be vigorously promoted. Therefore, to improve the efficiency of the oxygen evolution reaction (OER) at the anode, high-performance OER catalysts are essential. Given their advantages in electrocatalysis, nanoporous materials have garnered considerable attention in previous studies for OER applications. This review provides a comprehensive overview of various strategies to optimize active site utilization in nanoporous materials. These strategies include regulating pore size and porosity, constructing hierarchical nanoporous structures, and enhancing material conductivity. Additionally, it covers approaches to boost the intrinsic OER activity of nanoporous materials, such as tuning the composition of anions and cations, creating vacancies, constructing interfaces, and forming boundary active sites. While nanoporous materials offer significant potential for advancing OER, challenges remain, including difficulties in quantifying activity within nanopores, the unclear impact of nanoporous material morphology, challenges in accessing nanopore interiors with in situ techniques, and a lack of theoretical calculations on pore structure. However, these challenges also present opportunities, and we hope this review provides a fresh perspective to inspire future research.

Dynamically Stabilized Electronic Regulation and Electrochemical Reconstruction in Co and S Atomic Pair Doped Fe3 O4 for Water Oxidation

The electronic regulation and surface reconstruction of earth-abundant electrocatalysts are essential to efficient oxygen evolution reaction (OER). Here, an inverse-spinel Co,S atomic pair codoped Fe3 O4 grown on iron foam (Co,S-Fe3 O4 /IF) is fabricated as a cost-effective electrocatalyst for OER. This strategy of Co and S atomic pair directional codoping features accelerates surface reconstruction and dynamically stabilizes electronic regulation. CoS atomic pairs doped in the Fe3 O4 crystal favor controllable surface reconstruction via sulfur leaching, forming oxygen vacancies and Co doping on the surface of reconstructed FeOOH (Co-FeOOH-Ov /IF). Before and after surface reconstruction via in situ electrochemical process, the Fe sites with octahedral field dynamically maintains an appropriate electronic structure for OER intermediates, thus exhibiting consistently excellent OER performance. The electrochemically tuned Fe-based electrodes exhibit a low overpotential of 349 mV at a current density of 1000 mA cm-2 , a slight Tafel slope of 43.3 mV dec-1 , and exceptional long-term electrolysis stability of 200 h in an alkaline medium. Density functional theory calculations illustrate the electronic regulation of Fe sites, changes in Gibbs free energies, and the breaking of the restrictive scaling relation between OER intermediates. This work provides a promising directional codoping strategy for developing precatalysts for large-scale water-splitting systems.

Bimetallic Iron–Cobalt Catalysts and Their Applications in Energy-Related Electrochemical Reactions

Since the persistently increasing trend of energy consumption, technologies for renewable energy production and conversion have drawn great attention worldwide. The performance and the cost of electrocatalysts play two crucial roles in the globalization of advanced energy conversion devices. Among the developed technics involving metal catalysts, transition-metal catalysts (TMC) are recognized as the most promising materials due to the excellent properties and stability. Particularly, the iron–cobalt bimetal catalysts exhibit exciting electrochemical properties because of the interior cooperative effects. Herein, we summarize recent advances in iron–cobalt bimetal catalysts for electrochemical applications, especially hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). Moreover, the components and synergetic effects of the composites and catalytic mechanism during reaction processes are highlighted. On the basis of extant catalysts and mechanism, the current issues and prospective outlook of the field are also discussed.

A mesoporous C,N-co doped Co-based phosphate ultrathin nanosheet derived from a phosphonate-based-MOF as an efficient electrocatalyst for water oxidation

A mesoporous C,N-co doped Co-based phosphate ultrathin nanosheet derived from 2D phosphate MOFs has been explored and exhibits highly efficient OER performance.