Hierarchical Nanostructured Co–Mo–B/CoMoO_4–x Amorphous Composite for the Alkaline Hydrogen Evolution Reaction

Abstract

Transition metal borides (TMBs) are a class of important but less well-explored electrocatalytic materials for water splitting. The lack of an advanced methodology to synthesize complex nanostructured TMBs with tunable surface properties is a major obstacle to the exploration of the full potential of TMBs for electrocatalytic applications. Here, we report the facile fabrication of a cobalt foam (CF)-supported hierarchical nanostructured Co−Mo−B/CoMoO 4−x composite using a hydrothermal method, followed by annealing and NaBH 4 reduction treatments. Our study found that NaBH 4 reduction of CoMoO 4 resulted in the concurrent formation of amorphous Co−Mo−B and an O-vacancy-rich CoMoO 4−x substrate, which cooperatively catalyzed the hydrogen evolution reaction (HER) in an alkaline electrolyte. The hierarchical nanoporous structure derived from the dehydration and partial reduction reactions of the CoMoO 4 • nH 2 O precursor could offer ample accessible active sites, as well as interconnected channels for rapid mass transfer. In addition, the in situ growth of electrically conductive Co−Mo−B nanoparticles on the defective structured CoMoO 4−x substrate imparted the electrocatalyst with good electrical conductivity. As a result, the Co−Mo−B/CoMoO 4−x /CF catalyst showed impressively high activity and outstanding stability for the alkaline HER, outperforming most reported TMB electrocatalysts. For instance, it required an overpotential of 55 mV to afford 10 mA•cm −2 and showed a fluctuation of only ±8 mV in a 100 h constant-current test at 100 mA•cm −2 .

Amorphous Co-Mo-B Film: A High-Active Electrocatalyst for Hydrogen Generation in Alkaline Seawater

“…The Mo 3d spectrum of Co-Mo-B/NF in Figure 2 b can be deconvoluted to 227.7 eV for Mo 0 3d 5/2 . The peaks at 228.7 and 231.53 eV are well consistent with 3d 5/2 and 3d 3/2 of Mo 4+ , while two peaks at 234.24 and 235.3 eV are attributed to 3d 3/2 of Mo 6+ [ 34 , 38 , 39 ]. In terms of B 1s spectrum ( Figure 2 c), characteristic peaks at 187 and 191.8 eV are assigned to metallic and oxidized boron, respectively [ 34 ].…”

Defect and Interface Engineering of Three-Dimensional Open Nanonetcage Electrocatalysts for Advanced Electrocatalytic Oxygen Evolution Reaction

“…Splitting water via electricity is a promising strategy to effectively produce renewable hydrogen energy; however, inherently sluggish dynamics with a complicated four-electron transfer process for the oxygen evolution reaction (OER) proceeding at the anode demands a high overpotential to drive the reaction, resulting in large energy consumption and high cost. − It is difficult that the benchmark Ru/Ir-based catalysts meet large-scale practical applications due to their prohibitive costs, as well as disadvantageous environmental effects. − Currently, earth-abundant transition metal compounds, especially transition metal oxides (TMOs), have attracted increasing attention for serving as an alternative of Ru/Ir-based catalysts; however, most of these TMOs will exhibit limited OER activity because of unfavorable electronic structure and large electron transfer resistance. − With great endeavors devoted, the electrocatalytic performance of TMOs has been substantially improved; however, their performances are still unsatisfactory due to low intrinsic activity and limited active sites. − Rational combination of precious metals and TMOs via heterostructuring or doping could not only reduce the utilization of noble metals but also regulate the electronic properties of TMOs to boost the electrocatalytic reaction. − In addition, several strategies have also been proposed and applied for promoting the electrocatalytic OER activity of TMOs, including morphology regulation, interface engineering, phase control, heteroatom doping, and defect engineering. − Therein, interface engineering and defect engineering have been widely accepted as advanced pathways for tailoring surface and electronic properties at the atomic level. − On the one hand, rational interface engineering would create more accessible active sites, induce electronic and synergistic effects, and optimize surface chemical components. − On the other hand, the creation of surface defects would also exert remarkable influences on the binding strength between the intermediated species and defect sites, which is also essential to the OER activity. − However, simultaneous defect engineering and interface engineering in a TMO catalyst and a deep understanding of the structure–functional relationship are rarely reported.…”

Porous Nanoarchitectures of Nonprecious Metal Borides: From Controlled Synthesis to Heterogeneous Catalyst Applications

“…Therefore, controlled synthesis of porous TMBs with an amorphous–crystalline heterophase is of fundamental importance to take individual advantages of the amorphous and crystalline phases. An effective phase control strategy for obtaining amorphous–crystalline heterophase TMBs is by converting crystalline materials to partial amorphization by treating them with B-containing reagents . Treating the transition-metal oxide species with NaBH 4 can partially reduce M x+ and introduce B to the system, resulting in the partial amorphousness feature. , Figure b shows the preparation of Co 2 Fe-LDHs with a porous nanosheet–nanoflake structure, followed by the B-modified chemical reduction approach .…”