In Situ Preparation of Pt Nanoparticles Supported on N‑Doped Carbon as Highly Efficient Electrocatalysts for Hydrogen Production

We describe here that the electrode materials toward the hydrogen evolution reaction (HER) can be cathodically activated by anodic dissolution of Pt counter electrode, dependent on the nature of substrate materials and solution pH. It leads to a direct approach for in situ fabrication of a highly dispersed and active HER electrocatalyst with minimal Pt loading that requires only a piece of Pt (instead of Pt salt, such as K₂PtCl₆) as Pt source combined with judicious choices of substrate materials and electrolyte solution. For a typical sample obtained by pyrolyzing poly­(2,6-diaminopyridine) (PDAP) under ammonia atmosphere followed by successive cyclic voltammetry scans in 0.5 M H₂SO₄, a current density of 60 mA cm^–2 was obtained at an overpotential of only 50 mV. Although the Pt loading is only 1.5 wt % in the sample, this performance is even better than that of the commercial 20 wt % Pt/C. The experimental results indicate that the deposited Pt nanoparticles are highly dispersed on the electrode substrate with a size of 2–4 nm. Further experimental results suggest that the combination of three factors, including the slow release of Pt into solution, high specific surface area of the substrate materials, and homogeneously doped N atoms acting as Pt anchor sites, is the key for formation of the highly active Pt nanoparticles. This study thus also raises an alarm regarding the use of Pt counter electrode in HER catalysis, especially by N-doped carbon in an acidic solution

Hierarchically Structured Ni Nanotube Array-Based Integrated Electrodes for Water Splitting

The development of high-performance nonprecious electrocatalysts for overall water splitting has attracted increasing attention but remains a vital challenge. Herein, we report a ZnO-based template method to fabricate Ni nanotube arrays (NTAs) anchored on nickel foil for applications in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). On the basis of this precursor electrode, the three-dimensional NiSe₂ NTAs of unique sandwich-like coaxial structure have been fabricated by electrodeposition of NiSe₂ on Ni NTAs, which exhibits high performance toward the HER in both acidic and alkaline media. The method based on Ni NTAs can be readily extended to fabricate Ni₂P NTAs by gas–solid phosphorization for the HER, and NiFeO_<i>x</i> NTAs by anodic codeposition of Ni and Fe for the OER. Consequently, an alkaline electrolyzer has been constructed using NiFeO_<i>x</i> NTAs and NiSe₂ NTAs as anode and cathode, respectively, which can realize overall water splitting with a current density of 100 mA cm^–2 at an overpotential of 510 mV

Highly Dispersed Mo₂C Nanoparticles Embedded in Ordered Mesoporous Carbon for Efficient Hydrogen Evolution

The development of non-noble metal-based electrocatalysts for the hydrogen evolution reaction (HER) has attracted increasing attention over recent years. As a promising HER catalyst candidate, the preparation of molybdenum carbide requires high temperature for carbothermal reduction, which often causes nanoparticles sintering, leading to low exposed active sites. In this work, highly dispersed β-Mo₂C nanoparticles of approximately 5 nm embedded in ordered mesoporous carbon (Mo₂C@OMC) have been synergistically synthesized. During the synthesis process, the resol precursor for OMC template could serve as carbon source for the formation of Mo₂C and mitigate the sintering of Mo₂C nanoparticles. The resultant well-defined Mo₂C possesses highly exposed active sites of approximately 26.5% and exhibits an excellent performance for the HER in both acidic and alkaline solutions. The synthetic procedure developed in this study may be extended to fabricate other metal carbide@OMC nanocomposites for the HER and other electrocatalytic applications

N,P-Doped Molybdenum Carbide Nanofibers for Efficient Hydrogen Production

Molybdenum (Mo) carbide-based electrocatalysts are considered promising candidates to replace Pt-based materials toward the hydrogen evolution reaction (HER). Among different crystal phases of Mo carbides, although Mo₂C exhibits the highest catalytic performance, the activity is still restricted by the strong Mo–H bonding. To weaken the strong Mo–H bonding, creating abundant Mo₂C/MoC interfaces and/or doping a proper amount of electron-rich (such as N and P) dopants into the Mo₂C crystal lattice are effective because of the electron transfer from Mo to surrounding C in carbides and/or N/P dopants. In addition, Mo carbides with well-defined nanostructures, such as one-dimensional nanostructure, are desirable to achieve abundant catalytic active sites. Herein, well-defined N,P-codoped Mo₂C/MoC nanofibers (N,P-Mo_<i>x</i>C NF) were prepared by pyrolysis of phosphomolybdic ([PMo₁₂O₄₀]^3–, PMo₁₂) acid-doped polyaniline nanofibers at 900 °C under an Ar atmosphere, in which the hybrid polymeric precursor was synthesized via a facile interfacial polymerization method. The experimental results indicate that the judicious choice of pyrolysis temperature is essential for creating abundant Mo₂C/MoC interfaces and regulating the N,P-doping level in both Mo carbides and carbon matrixes, which leads to optimized electronic properties for accelerating HER kinetics. As a result, N,P-Mo_<i>x</i>C NF exhibits excellent HER catalytic activity in both acidic and alkaline media. It requires an overpotential of only 107 and 135 mV to reach a current density of 10 mA cm^–2 in 0.5 M H₂SO₄ and 1 M KOH, respectively, which is comparable and even superior to the best of Mo carbide-based electrocatalysts and other noble metal-free electrocatalysts