N-doped Carbon-coated Metal Sulfides/Phosphides Derived from Protic Salts for Oxygen Evolution Reaction

Design of NiCoP nanorod loaded on cocoon carbon substrate and its non-metal doping for efficient hydrogen evolution

The quest for effective and sustainable electrocatalysts for hydrogen evolution is crucial in advancing the widespread use of H2. In this study, we utilized silkworm cocoons as the source material to produce porous N-doped carbon (PNCC) substrates through a process involving degumming and annealing. Subsequently, NiCoP nanorod (NiCoP@PNCC) is deposited onto the substrates via a simple impregnation and calcination method to enhance the catalytic performance for the hydrogen evolution reaction (HER). The optimal spacing between the silk fibers of PNCC facilitates longitudinal growth, increases the active surface area, and balances the adsorption and desorption of reaction intermediates, thereby accelerating HER kinetics. Consequently, NiCoP@PNCC demonstrates impressive performance, with 44 mV overpotential to achieve a current density of 10 mA cm-2. Additionally, density functional theory (DFT) calculations reveal that the electronic structure and energy band of NiCoP@PNCC can be modified through the doping of elements such as B, C, N, O, F, and S. In addition, with the electronegativity enhancement of the doping elements, the interaction between Co atoms in NiCoP@PNCC and O atoms in adsorbed H2O molecules gradually enhanced, which is conducive to the dissociation of water in alkaline solution. This research introduces a novel approach for fine-tuning the catalytic activity of transition metal phosphides.

Loading of Single Atoms of Iron, Cobalt, or Nickel to Enhance the Electrocatalytic Hydrogen Evolution Reaction of Two-Dimensional Titanium Carbide

The rational design of advanced electrocatalysts at the molecular or atomic level is important for improving the performance of hydrogen evolution reactions (HERs) and replacing precious metal catalysts. In this study, we describe the fabrication of electrocatalysts based on Fe, Co, or Ni single atoms supported on titanium carbide (TiC) using the molten salt method, i.e., TiC-FeSA, TiC-CoSA, or TiC-NiSA, to enhance HER performance. The introduction of uniformly distributed transition-metal single atoms successfully reduces the overpotential of HERs. Overpotentials of TiC-FeSA at 10 mA cm-2 are 123.4 mV with 61.1 mV dec-1 Tafel slope under acidic conditions and 184.2 mV with 85.1 mV dec-1 Tafel slope under alkaline conditions, which are superior to TiC-NiSA and TiC-CoSA. TiC samples loaded with transition-metal single atoms exhibit high catalytic activity and long stability under acidic and basic conditions. Density functional theory calculations indicate that the introduction of transition-metal single atoms effectively reduces the HER barrier of TiC-based electrocatalysts.

A Review of Transition Metal Boride, Carbide, Pnictide, and Chalcogenide Water Oxidation Electrocatalysts

Transition metal borides, carbides, pnictides, and chalcogenides (X-ides) have emerged as a class of materials for the oxygen evolution reaction (OER). Because of their high earth abundance, electrical conductivity, and OER performance, these electrocatalysts have the potential to enable the practical application of green energy conversion and storage. Under OER potentials, X-ide electrocatalysts demonstrate various degrees of oxidation resistance due to their differences in chemical composition, crystal structure, and morphology. Depending on their resistance to oxidation, these catalysts will fall into one of three post-OER electrocatalyst categories: fully oxidized oxide/(oxy)hydroxide material, partially oxidized core@shell structure, and unoxidized material. In the past ten years (from 2013 to 2022), over 890 peer-reviewed research papers have focused on X-ide OER electrocatalysts. Previous review papers have provided limited conclusions and have omitted the significance of "catalytically active sites/species/phases" in X-ide OER electrocatalysts. In this review, a comprehensive summary of (i) experimental parameters (e.g., substrates, electrocatalyst loading amounts, geometric overpotentials, Tafel slopes, etc.) and (ii) electrochemical stability tests and post-analyses in X-ide OER electrocatalyst publications from 2013 to 2022 is provided. Both mono and polyanion X-ides are discussed and classified with respect to their material transformation during the OER. Special analytical techniques employed to study X-ide reconstruction are also evaluated. Additionally, future challenges and questions yet to be answered are provided in each section. This review aims to provide researchers with a toolkit to approach X-ide OER electrocatalyst research and to showcase necessary avenues for future investigation.

Versatile Synthesis of Carbon Materials using Protic Ionic Liquids and Salts as Precursors

Carbon materials (CMs) hold immense potential for applications across a wide range of fields. However, current precursors often confront limitations such as low heteroatom content, poor solubility, or complicated preparation and post-treatment procedures. Our research has unveiled that protic ionic liquids and salts (PILs/PSs), generated from the neutralization of organic bases with protonic acids, can function as economical and versatile small-molecule carbon precursors. The resultant CMs display attractive features, including elevated carbon yield, heightened nitrogen content, improved graphitic structure, robust thermal stability against oxidation, and superior conductivity, even surpassing that of graphite. These properties can be elaborate modulated by varying the molecular structure of PILs/PSs. In this Personal Account, we summarize recent developments in PILs/PSs-derived CMs, with a particular focus on the correlations between precursor structure and the physicochemical properties of CMs. We aim to impart insights into the foreseeable controlled synthesis of advanced CMs.