Anion Modulation of Pt-Group Metals and Electrocatalysis Applications

Screening of single-atomic catalysts loaded on two-dimensional transition metal dichalcogenides for electrocatalytic oxygen reduction via high throughput ab initio calculations

The design and screening of low cost and high efficiency oxygen reduction reaction (ORR) electrocatalysts is vital in the realms of fuel cells and metal-air batteries. Existing studies largely rely on the calculation of absorption free energy, a method established 20 years ago by Jens K. Nørskov. However, the study of electrocatalysts grounded solely on free energy calculation often lacks in-depth analysis, particularly overlooking the influence of solvent and electrode potential. In this regard, we here present a novel approach using constant-potential and ab initio molecular dynamics (AIMD) simulation to screen single-atom catalysts loaded on transition metal dichalcogenides (SA@TMDs) for ORR. An extensive investigation of 1584 SA@TMDs results in 20 high performing ORR catalysts with overpotential less than 0.33 V and high working stability. In addition, our study shows that the electrode potential has different effects on the adsorption energy of *OOH, *O and *OH, which leads to a reversal of the rate-determining step (RDS) of the ORR. This work presents not only credible, high-performance catalyst candidates for experimental exploration, but also significantly improves our understanding on the reaction mechanism of ORR under realistic reaction conditions.

S-S Bond Strategy at Sulfide Heterointerface: Reversing Charge Transfer and Constructing Hydrogen Spillover for Boosted Hydrogen Evolution

Developing efficient electrocatalyst in sulfides for hydrogen evolution reaction (HER) still poses challenges due to the lack of understanding the role of sulfide heterointerface. Here, we report a sulfide heterostructure RuSx/NbS2, which is composed of 3R-type NbS2 loaded by amorphous RuSx nanoparticles with S-S bonds formed at the interface. As HER electrocatalyst, the RuSx/NbS2 shows remarkable low overpotential of 38 mV to drive a current density of 10 mA cm-2 in acid, and also low Tafel slope of 51.05 mV dec-1. The intrinsic activity of RuSx/NbS2 is much higher than that of Ru/NbS2 reference as well as the commercial Pt/C. Both experiments and theoretical calculations unveil a reversed charge transfer at the interface from NbS2 to RuSx that driven by the formation of S-S bonds, resulting in electron-rich Ru configuration for strong hydrogen adsorption. Meanwhile, electronic redistribution induced by the sulfide heterostructure facilitates hydrogen spillover (HSo) effect in this system, leading to accelerated hydrogen desorption at the basal plane of NbS2. This study provides an effective S-S bond strategy in sulfide heterostructure to synergistically modulate the charge transfer and adsorption thermodynamics, which is very valuable for the development of efficient electrocatalysts in practical applications.

Molten Salt-Assisted Synthesis of Catalysts for Energy Conversion

A breakthrough in manufacturing procedures often enables people to obtain the desired functional materials. For the field of energy conversion, designing and constructing catalysts with high cost-effectiveness is urgently needed for commercial requirements. Herein, the molten salt-assisted synthesis (MSAS) strategy is emphasized, which combines the advantages of traditional solid and liquid phase synthesis of catalysts. It not only provides sufficient kinetic accessibility, but effectively controls the size, morphology, and crystal plane features of the product, thus possessing promising application prospects. Specifically, the selection and role of the molten salt system, as well as the mechanism of molten salt assistance are analyzed in depth. Then, the creation of the catalyst by the MSAS and the electrochemical energy conversion related application are introduced in detail. Finally, the key problems and countermeasures faced in breakthroughs are discussed and look forward to the future. Undoubtedly, this systematical review and insights here will promote the comprehensive understanding of the MSAS and further stimulate the generation of new and high efficiency catalysts.

Tailoring the Coordination Micro-Environment in Nanotraps for Efficient Platinum/Palladium Separation

Recovering platinum group metals from secondary resources is crucial to meet the growing demand for high-tech applications. Various techniques are explored, and adsorption using porous materials has emerged as a promising technology due to its efficient performance and environmental beingness. However, the challenge lies in effectively recovering and separating individual platinum group metals (PGMs) given their similar chemical properties. Herein, a breakthrough approach is presented by sophisticatedly tailoring the coordination micro-environment in a series of aminopyridine-based porous organic polymers, which enables the creation of platinum-specific nanotraps for efficient separation of binary PGMs (platinum/palladium). The newly synthesized POP-o2NH2-Py demonstrates record uptakes and selectivity toward platinum over palladium, with the amino groups adjacent to the pyridine moieties being vital in improving platinum binding performance. Further breakthrough experiments underline its remarkable ability to separate platinum and palladium. Spectroscopic analysis reveals that POP-o2NH2-Py offers a more favorable coordination fashion to platinum ions compared to palladium ions owing to the greater interaction between N and Pt4+ and stronger intramolecular hydrogen bonding between the amino groups and four coordinating chlorines at platinum. These findings underscore the importance of fine-tuning the coordination micro-environment of nanotraps through subtle modifications that can greatly enhance the selectivity toward the desired metal ions.

Fe-Regulated Amorphous-Crystal Ni(Fe)P2 Nanosheets Coupled with Ru Powerfully Drive Seawater Splitting at Large Current Density

Water electrolysis is an ideal method for industrial green hydrogen production. However, due to increasing scarcity of freshwater, it is inevitable to develop advanced catalysts for electrolyzing seawater especially at large current density. This work reports a unique Ru nanocrystal coupled amorphous-crystal Ni(Fe)P2 nanosheet bifunctional catalyst (Ru-Ni(Fe)P2 /NF), caused by partial substitution of Fe to Ni atoms in Ni(Fe)P2 , and explores its electrocatalytic mechanism by density functional theory (DFT) calculations. Owing to high electrical conductivity of crystalline phases, unsaturated coordination of amorphous phases, and couple of Ru species, Ru-Ni(Fe)P2 /NF only requires overpotentials of 375/295 and 520/361 mV to drive a large current density of 1 A cm-2 for oxygen/hydrogen evolution reaction (OER/HER) in alkaline water/seawater, respectively, significantly outperforming commercial Pt/C/NF and RuO2 /NF catalysts. In addition, it maintains stable performance at large current density of 1 A cm-2 and 600 mA cm-2 for 50 h in alkaline water and seawater, respectively. This work provides a new way for design of catalysts toward industrial-level seawater splitting.

Agarose-gel-based self-limiting synthesis of a bimetal (Fe and Co)-doped composite as a bifunctional catalyst for a zinc-air battery

Exploring efficient noble-metal-free electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is crucial for the development of rechargeable Zn-air batteries. Herein, a self-limiting method using an agarose gel was proposed to prepare bimetallic (iron and cobalt) nitrogen-doped carbon composites (FeCo-NC). The resulting FeCo-NC catalyst has a high surface area and a hierarchical porous structure. The optimized FeCo-NC electrocatalyst exhibits a small potential difference (ΔE) = 0.72 V between the ORR half-wave potential and the OER potential at a current density of 10 mA cm^-2 in alkaline media. Impressively, the FeCo-NC Zn-air battery exhibits a high open-circuit voltage, large power density, and outstanding charge-discharge cycling stability. This study provides an effective means of designing electrocatalysts and energy conversion systems.