Metastable Phase-Controlled Synthesis of Mesoporous Molybdenum Carbides for Efficient Alkaline Hydrogen Evolution

Abstract

Transition metal carbides (TMCs) have shown great promise as nonprecious metal electrocatalysts for electrochemical energy conversion reactions owing to their Pt-like catalytic activity. The major challenges in the synthesis of TMCs include the selective formation of a catalytically active phase, enlargement of the catalytically active surface area, and control of the carbonaceous overlayer, all of which collectively influence their catalytic reactivity. Herein, we present a systematic study on the catalytically active metastable phase-selective synthesis of mesoporous molybdenum carbides with controlled carbon overlayer thickness for efficient alkaline hydrogen evolution reaction (HER) electrocatalysis. The synthesis of molybdenum carbides was explored by controlling the types of Mo and C precursors and carburization conditions and the use of a mesoporous silica template. The choice of the Mo precursor and the nanospace-confined carburization were identified as critical factors for the formation of mesoporous molybdenum carbides of the metastable α-MoC1–x phase (MMC) with a large catalytically active surface area. The thickness of the carbon overlayer on the surfaces of the molybdenum carbides increased proportionally with the carburization temperature and decreased substantially with H2 post annealing. Among the prepared catalysts, the H2-annealed MMC (MMC-H2) exhibited the highest alkaline HER activity and reaction kinetics, which is one of the best among the meal carbide alkaline HER catalysts reported so far and compared favorably with a commercial Pt/C catalyst. The MMC-H2 also demonstrated superior durability and stability as compared to MMC and Pt/C catalysts.

Non‐siliceous ordered mesoporous materials via nanocasting for small molecule conversion electrocatalysis

“…(e) Polarization curves of MMC‐H 2 , MMC, and 20 wt% Pt/C catalysts recorded before and after 1000 cycles between 0.1 and −0.3 V (vs. RHE). Reproduced from Baek et al 40 with permission from the ACS. (f) HRTEM image of Pt/MMC with structural model.…”

“…Inspired by these results, we attempted to prepare a large surface area metastable α ‐MoC 1− x material to boost the alkaline HER activity 40 . Toward realizing this goal, nanocasting again proved to be a versatile method.…”

“…This account presents our decade‐long efforts in the direction of the function‐oriented design of OMMs for promoting electrocatalytic reactions relevant to renewable energy conversion and commodity chemical production. We prepared a wide range of non‐siliceous OMMs via nanocasting, which are composed of carbons, 26,27 heteroatom‐doped carbons, 26,28,29 carbon nitrides, 30 OMC–carbon nanotube (CNT), 31,32 transition metal and nitrogen co‐doped carbons (M–N/C), 33–35 metal alloys and intermetallic structures, 36,37 metal oxides, 38 metal carbides, 39,40 and metal sulfides 41,42 (Figure 1). The OMMs were exploited as advanced electrocatalysts for HER, 4e − /2e − pathway ORR, and OER (Figure 1, left bottom).…”

B4C enhances the supported platinum DER/HER performance

“…The support has the role of dispersing and anchoring the active component, and the interaction force between different supports and the active component varies; thus, the choice of support is equally important. Carbides have been widely studied as typical electrocatalytic supports, 23,24 including carbides such as Mo 2 C, 25–28 WC, 29,30 TiC, 31 and Ni 3 C; 32 they have stronger interactions with metals than carbon, 33 and can provide stronger interaction forces. Among them, boron carbide (B 4 C) is a nonmetallic carbide; it is one of the most stable substances toward acid and has the advantages of a high melting point and good electrical conductivity.…”

Computationally Guided Design to Accelerate Discovery of Doped β-Mo2C Catalysts toward Hydrogen Evolution Reaction

“…Mo y C can be stabilized into several phases including α-Mo 2 C, β-Mo 2 C, α-MoC, γ-MoC, δ-MoC, and η-MoC. − Among these phases, β-Mo 2 C is found to be the most catalytically active phase. , In a previous study, we showed that the active sites of β-Mo 2 C originate from the (011) surface that exposes Mo–C atoms, as it has low surface energy and can bind hydrogen optimally . In the last few years, considerable attention has been devoted to further improving the HER efficiency of Mo y C catalysts via a complex nanostructuring approach that involves a hybrid of several mechanisms.…”