Tungsten Carbide Encapsulated in Grape-Like N-Doped Carbon Nanospheres: One-Step Facile Synthesis for Low-Cost and Highly Active Electrocatalysts in Proton Exchange Membrane Water Electrolyzers

Abstract

Tungsten carbide (WC) is an alternative to the costly and resource-constrained Pt-based catalysts. Herein, a one-step facile and easily scalable approach is reported to synthesize ultrafine WC nanocrystals encapsulated in porous N-doped carbon nanospheres (NC) by simple self-polymerization, drying, and annealing. It is worth mentioning that this developed method has four novel features: (1) the synthesis process, without any hard template or hydrocarbon gas feeding, is, notably, very facile and efficient with low cost; (2) the carbon coating on WC nanocrystals not only restrains coarsening of particles but also creates strong coupling interactions between the nanocrystallines and the conductive carbonaceous matrix; (3) uniform grape-like WC@NC nanospheres with high specific surface area can be obtained in a large scale; and (4) single-phase WC can be achieved. As a result, WC@NC demonstrates remarkable hydrogen evolution reaction (HER) electrocatalytic performance with overpotentials of 127 and 141 mV at a current density of 10 mA cm–2 and Tafel slopes of 56.3 and 78.7 mV dec–1 in acid and alkaline media, respectively. Our density functional theory calculations manifest that the strong synergistic electronic effect between WC and its intimately bonded carbon shell vastly boosts the HER electrocatalytic activity. WC@NC catalysts as a cathode are further tested in a home-made electrolyzer with 0.78 A cm–2 achieved at a cell voltage of 2 V at 80 °C and operated stably at 200 mA cm–2 for more than 20 h.

Facile electrochemical preparation of nonprecious Co‐Cu alloy catalysts for hydrogen production in proton exchange membrane water electrolysis

“…The performance of CoCu/CP was then evaluated (Figure C) by first applying 2.3 V cell for 20 minutes and then applying a constant current density in the range of 0.02 to 2.0 A cm −2 . This cell showed excellent performance of 1.2 A cm −2 at 2.0 V cell , which is superior to the performance of electrolyzers using other non‐Pt catalysts shown in Figure D (FeCoP: 0.95 A cm −2 , WC@NC: 0.78 A cm −2 , CuMo: 0.73 A cm −2 , NiCoOS: 0.72 A cm −2 , and FeS 2 /C: 0.56 A cm −2 ,). In addition, the performance of the Co‐Cu alloy catalyst is similar or slightly lower than that of NiP (1.31 A cm −2 ), Mo@Ru (1.156 A cm −2 ), and MoP|S‐CB (1.14 A cm −2 ) and is approximately 39% to 60% of that of Pt‐based PEMWEs (3.1, 2.69, 2.25, and 2.0 A cm −2 ).…”

Catalyst overcoating engineering towards high-performance electrocatalysis

“…392 Combining the merits of the carbon matrix with nonprecious metal species by using various overcoating methodologies, along with the phosphorization or sulfurization treatment, promises cost-effective electrocatalysts based on abundant metals for efficient overall water splitting reactions. Recently, boosting research activities have been dedicated to the development of surface overcoating-derived bifunctional overall water splitting electrocatalysts, including metallic transition metals and alloys, 117,324,345,[393][394][395][396][397][398] transition metal (hydro)oxides, 144,[399][400][401][402] metal phosphides, 130,131,327,[403][404][405][406] metal carbides [407][408][409] and metal chalcogenides. 101,410,411 Some typical examples of these works are presented below.…”

Heteroatom-Doped Metal-Free Carbon Nanomaterials as Potential Electrocatalysts

“…Furthermore, these carbon nanodots were subsequently immobilized onto functionalized microporous carbon nanospheres (MCNSs) with an average diameter of ∼100 nm and a surface area of 241 m 2 g −1 via a simple hydrothermal process to self-assemble a carbon-based nanocomposite (N-CNDs@MCNSs) in the presence of oxygen (O)-containing surface functional groups [132]. Today, a significant number of research works were carried out on nitrogen encapsulation on metal/metal oxides/carbon nanosphere materials potentially applied as electrodes or electrocatalysts [133][134][135][136][137][138][139][140]. In the current review, those works were not considered, as they are not metal-free nanostructured materials.…”