Tuning the Ni/Co Ratios and Surface Concentration of Reduced Molybdenum States for Enhanced Electrocatalytic Performance in Trimetallic Molybdates: OER, HER, and MOR Activity

Abstract

The heterogeneous nature of trimetallic catalyst systems comes with beneficial synergy for catalytic applications. Nonetheless, the challenges associated to validate and control the critical characteristics for enhanced electrocatalytic efficiencies are yet to be known. Herein, a genre of trimetallic catalysts were synthesized with Ni, Co, and Mo metals, whose morphological, structural, electronic, and interface properties depend on Ni/Co and Mo+4/Mo+5 ratios and the dominant element on the surface of the catalyst. The results suggest that introduction of a third metal, that is, Mo, is only beneficial when the Ni/Co ratio is optimally maintained. By combining the surface electronic and structural analyses such as electron energy loss spectroscopy, X-ray photoelectron spectroscopy, line scan, Raman spectra, and electrochemical data, it was realized that Mo and metallic Ni on the surface favor oxygen evolution reaction (OER), and methanol oxidation reaction (MOR) activity, respectively. Interestingly, the adsorbed water molecules were found to be vital for higher performance in both OER and MOR processes. The chronopotentiometry tests performed with the optimized catalyst Ni56Co7Mo37 for OER showed an overpotential around ca. 309 mV at ca. 720 mA·cm–2 even after 17 h (and also a Tafel slope of 60 mV·dec–1 at 10 mA·cm–2). The peak current density (from the cyclic voltammetry tests) in the optimized catalyst, that is, Ni66Co31Mo3 (for MOR), showed almost 300-fold higher activity in 1 M KOH + 1 M CH3OH solution when compared with only 1 M KOH. Further, comparative studies were also conducted with bimetallic catalysts of Ni, Co, and Mo to understand the better combinations for promoting OER, hydrogen evolution reaction, and MOR efficiencies. This work highlights the importance of maintaining the elemental composition ratios at the bulk and surface that lead to an active environment for OER and MOR processes and thereby opening gateways for a rational design of trimetallic electrocatalysts.

Trimetallic Ni–Co–Mo Nanoparticles Supported on N-Doped Carbon as a Promising Electrocatalyst for the Methanol-Assisted Hydrogen Evolution Reaction

“…At current densities of 10, 50, 100, and 150 mA cm –2 , the 450-NCMO@NC catalyst displays low overpotentials of 92, 220, 290, and 345 mV, respectively. These values are significantly better than those of the other prepared catalysts and most previously reported transition-metal-based catalysts. ,,– In contrast, the 400-NCMO@NC sample exhibits overpotentials of 130, 350, 460, and 544 mV, while the 500-NCMO@NC sample shows overpotentials of 217, 392, 520, and 632 mV at the same current densities. To comprehensively assess the comparative HER activity, we have also included the LSV curves of the control samples NiMoO 4 /NC (450-NMO/NC) and CoMoO 4 /NC (450-CMO/NC).…”

“…In Figure b, the Ni 2p spectrum of 450-NCMO@NC is deconvoluted into two main peaks located at 854.1 eV, corresponding to NiO, and at 855.9 eV, assigned to Ni 2p 3/2 of the Ni 2+ oxidation state. Additionally, an additional satellite peak at 861.4 eV corresponds to Ni 2p 3/2 of the Ni 3+ oxidation state, , indicating the presence of oxidized Ni species (Ni­(OH) 2 and Ni–O) on the surface. , The presence of Ni 0 , as indicated by XPS analysis, is likely attributed to the utilization of sodium borohydride (NaBH 4 ) as a reducing agent during the material synthesis process. This agent has the potential to facilitate the reduction of specific Ni salts or oxides to a zero oxidation state, thereby facilitating the integration of metallic Ni into the composite structure.…”

“…These findings confirm the coexistence of CoMoO 4 and NiMoO 4 phases, consistent with the XRD pattern (Figure 2). Furthermore, high-angle annular dark-field (HAADF) mapping, presented in Figure S1 47,48 The presence of Ni 0 , as indicated by XPS analysis, is likely attributed to the utilization of sodium borohydride (NaBH 4 ) as a reducing agent during the material synthesis process. This agent has the potential to facilitate the reduction of specific Ni salts or oxides to a zero oxidation state, thereby facilitating the integration of metallic Ni into the composite structure.…”

A Review on Low-Dimensional Nanomaterials: Nanofabrication, Characterization and Applications

“…During photocatalytic reactions, photo-induced electrons and holes can trigger the production of reactive oxygen species, which in turn leads to hydrogen evolution reaction and oxygen reduction reaction [ 251 ]. These reactive species are also useful to eliminate contamination in our environment, such as organic dye molecules and residual antibiotic [ 252 , 253 , 254 ].…”

Preparation of carbon coated hyperdispersed Ru nanoparticles supported on TiO2 HER electrocatalysts by dye-sensitization

“…[6][7][8][9] In recent years, people have done a lot of research work on the development of alternative platinum based HER electrocatalysts, and a large number of representative new catalysts have emerged, such as low-platinum, non-platinum, nonprecious metal and metal-free types. [10][11][12] One of the common methods is to reduce the amount of precious metal platinum and design low-platinum catalysts such as core-shell (the shell is a thin layer of platinum), alloy (Pt-M, M represents Ru, Pd, Co, Ni, Fe, etc.) and single-atom catalysts (SACs).…”