Cobalt-Vanadium Layered Double Hydroxides Nanosheets as High-Performance Electrocatalysts for Urea Oxidation Reaction

Abstract

Hydrogen is considered as a desirable clean energy source for supporting human life in the future. Electrochemical water splitting is a promising method for generating carbon-free hydrogen. However, the relatively high overpotential of anodic oxygen evolution reaction (OER) is the main obstacle hindering the widespread popularity of water electrocatalysis technology. Recently, urea oxidation reaction (UOR) has gained significant attention as a potential alternative to OER for hydrogen production since the equilibrium potential of UOR is 0.86 V lower than that of OER. Transition metal-based layered double hydroxides (TM-LDHs) have been explored as promising UOR electrocatalysts, with the advantages of diversified metal species, stable twodimensional layered structure and exchangeability of interlayer anions. To date, most studies have focused on TM-LDHs of late transition metals (e.g., Ni, Co, and Fe). In this work, by combining early and late transition metals, CoV-LDHs nanosheets were fabricated via a simple one-step coprecipitation method as high-performance UOR electrocatalysts. Additionally, cobalt hydroxide (Co(OH)2), with a similar lamellar structure, was synthesized via the same method. When compared with Co(OH)2, CoV-LDHs nanosheets exhibited better UOR performance owing to the following advantages: 1) The nanosheet structure of the as-fabricated CoV-LDHs electrocatalyst exposed a high number of active sites for the electrocatalytic conversion of urea. 2) The introduction of V enhanced the wettability of the CoV-LDHs electrocatalyst; thus, increasing its intrinsic electrocatalytic kinetics. 3) The d-electron compensation effect between Co (3d 7 4s 2 ) and V (3d 3 4s 2 ) was conducive to promoting the adsorption of urea. Therefore, the CoV-LDHs electrocatalyst exhibited a low electrochemical potential (1.52 V vs. the reversible hydrogen electrode, RHE) to achieve a current density of 10 mA•cm -2 in 1 mol•L −1 of potassium hydroxide containing 0.33 mol•L −1 urea, which was 70 mV less than that of Co(OH)2. The Tafel slope value of the CoV-LDHs electrocatalyst (99.9 mV•dec −1 ) was lower than that of Co(OH)2 (115.9 mV•dec −1 ), indicating faster UOR kinetics over the CoV-LDHs electrocatalyst. Furthermore, the CoV-LDHs electrocatalyst displayed high stability, with a negligible potential increase after a 10-h chronopotentiometry test by maintaining the current density of 10 mA•cm −2 . In conclusion, the present work not only shows that the d-electron compensation effect between early and late transition metals could adjust the local electronic structure of TM-LDHs to improve the UOR efficiency, but also provides a feasible route to design dedicated nanostructured TM-LDHs as high-performance UOR electrocatalysts.

The structural feature of Ni–Al-LDH nanosheets and their adsorption performance for ethyl mercaptan from methane gas

“…36–38 Lamellar typical diffraction peaks of (003) and (006) in Ni–Al-LDH-NS no longer exist, revealing that Ni–Al-LDH-NS no longer possesses a lamellar structure but rather a sheet structure. 39–41 However, the typical diffraction peaks of (110) still exist and the locations is stable, which means that Ni–Al-LDH-NS is still a two-dimensional nanomaterial. 41 The typical diffraction peaks (015), (018), (113) and (116) disappeared, while the peak corresponding to the (012) plane still existed.…”

“…The phase and structure of the material is evaluated using XRD analysis, as shown in [36][37][38] Lamellar typical diffraction peaks of ( 003) and (006) in Ni-Al-LDH-NS no longer exist, revealing that Ni-Al-LDH-NS no longer possesses a lamellar structure but rather a sheet structure. [39][40][41] However, the typical diffraction peaks of (110) still exist and the locations is stable, which means that Ni-Al-LDH-NS is still a twodimensional nanomaterial. 41 The typical diffraction peaks (015), (018), ( 113 and after Ethyl Mercaptan adsorption, which means that EM does not enter the interlayer, but is adsorbed on the outer surface of the material.…”

CoFe-Layered Double Hydroxide Needles on MoS2/Ni3S2 Nanoarrays for Applications as Catalysts for Hydrogen Evolution and Oxidation of Organic Chemicals

“…Some studies have shown that Ni 3+ can be regarded as the active center to promote the oxidation of the urea molecule . Nickel-rich Ni 3 S 2 with abundant Ni–S and Ni–Ni bonds drive the formation of UOR intermediates (OOH*). , Layered double hydroxides (LDHs) are capable of producing surface hydroxides as active substances to optimize the H 2 O dissociation process. − As a member of the LDH family, CoFe LDH is often used to improve the OER performance of catalysts. − Furthermore, many studies have reported that one-dimensional (1D) nanostructures enhanced electrocatalytic performances attributed to their increased specific surface area and active exposed sites, which facilitate ion transport, diminish the diffusion paths of electrolytes, and consequently reduce the cost of electrocatalysts. − …”

PtxAg100−x nano-alloy decorated N-doped reduced graphene oxide: a promising electrocatalyst for direct urea fuel cells

“…Enormous research efforts are being invested for the design and development of UOR specific electrocatalysts. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] However, limitations like low electrical conductivity, stability/tolerance toward poisonous reaction intermediates, low experimental energy density, high cost, poor durability, and limited availability of the to date reported electrocatalysts continue to impede the development of practically useful DUFCs. 6,7 Metal catalysts viz.…”

“…6,7 Metal catalysts viz. Pt/C, Ag/C, Ti-Pt, Ti-Pt-Ir, Ru, 6,7 Ni/C, 12 Pd 10% Ni 10% , 13 Ni (10%) Pd (10%) /OMC, and IrO@C, 14 including recently developed non-noble Ni and Cobased 6,12,13,19 UOR catalysts, exhibit many limitations that negate their suitability for practical applications. These limitations include a low tolerance toward poisoning, high overpotential requirements, low current/power densities, insufficient output voltages, and inadequate stability.…”