Insights into the Mo-Doping Effect on the Electrocatalytic Performance of Hierarchical Co_xMo_yS Nanosheet Arrays for Hydrogen Generation and Urea Oxidation

Abstract

Energy-efficient, low-cost, and highly durable catalysts for the electrochemical hydrogen evolution reaction (HER) and urea oxidation reaction (UOR) are extremely important for related sustainable energy systems. In the present work, hierarchical coassembled cobalt molybdenum sulfide nanosheets deposited on carbon cloth (CC) were synthesized as catalysts for hydrogen evolution and urea oxidation. By adjusting the doping amount of Mo, 2D nanosheets with different morphologies and compositions (Co x Mo y S-CC) can be obtained. The as-prepared nanosheet materials with abundant active sites exhibit superior properties on the electrochemical HER and UOR in alkaline medium. Significantly, the Mo-doping concentration and composition of the formed nanosheets have large effects on the electrocatalytic activity. The fabricated nanosheets with optimal Mo doping (Co3Mo1S-CC) illustrate the best catalytic properties for the HER in N2-saturated 1.0 M KOH. A small overpotential (85 mV) is needed to meet the current density of 10 mA/cm2. This study indicates that the doping of an appropriate amount of molybdenum into CoS2 nanosheets can efficiently improve the catalytic performance. Also, the nanosheet catalyst exhibits an extremely high electrocatalytic activity for the UOR, and the electrochemical results indicate that a relatively low cell voltage of 1.50 V is needed to obtain the current density of 10 mA/cm2. The present work demonstrates the potential application of CoMoS nanosheets in the energy electrocatalysis area and the insights into performance-boosting through heteroatom doping and optimization of the composition and structure.

Oxygen‐Deficient Cobalt‐Based Oxides for Electrocatalytic Water Splitting

“…The electrons in the delocalized electronic structure can be easily excited into the conduction band, [19] which leads to faster charge separation and transfer (enhanced conductivity). All the aforementioned effects minimize the overpotential and facilitate electrochemical water splitting [7,16a,b,20] …”

Co(OH)2 Nanosheets Array Doped by Cu2+ Ions with Optimal Electronic Structure for Urea‐Assisted Electrolytic Hydrogen Generation

“…Considering the potential for the oxidation of Co 2 + to Co 3 + is lower than that of Ni 2 + to Ni 3 + , the Co-based materials are more likely favorable for UOR electrocatalysis. Although several Co-based materials, including layer double hydroxides (LDH), [17,18] chalcogenides, [7,19] and phosphides, [20] have been applied in urea-assisted electrolytic hydrogen generation, they still undergo the unsatisfactory electrocatalytic performances, especially at large current densities. Therefore, it is necessary to construct Co-based catalysts with optimal structure for high-performance electrocatalysis toward UOR and HER.…”

“…Urea oxidation reaction (UOR) has the advantage of a lower thermodynamical theoretical voltage of 0.37 V than that of 1.23 V for OER [6] . Therefore, UOR is a favorable substitution for sluggish OER for energy‐saving hydrogen generation, accompanying by simultaneous urea‐containing wastewater remediation with non‐toxic oxidized products of CO 2 and N 2 [7] . Nevertheless, the bottleneck of UOR is its inherent sluggish six‐electron transfer process, which makes overall urea electrolysis still face low activity and high potential [8] .…”

High‐efficiency electrolysis of biomass and its derivatives: Advances in anodic oxidation reaction mechanism and transition metal‐based electrocatalysts

“…At the same time, the authors pointed out that the redox active species to promote the conversion of primary amine to nitrile are Ni II /Ni III on the surface of the NiSe electrode. Other examples of transitional metal chalcogenides based catalysts employed for UOR include Co x Mo y S nanosheet in which the variation in Mo doping affects its catalytic property significantly [77] and porous nickel cobalt sulfide nanosheet array on the carbon cloth (NiCo 2 S 4 /CC) that exhibited good reaction kinetics due to the inherent high activity and synergistic effect of Ni and Co, as well as the rapid electron mass transfer enabled by the abundant active sites. [78] Diversity of the transitional metal compounds used in BEORs has even been extended to phosphides, nitrides, and borides.…”