Metallic Nickel Hydroxide Nanosheets Give Superior Electrocatalytic Oxidation of Urea for Fuel Cells

Abstract

The direct urea fuel cell (DUFC) is an important but challenging renewable energy production technology,i to ffers great promise for energy-sustainable developments and mitigating water contamination. However,DUFCs still suffer from the sluggish kinetics of the urea oxidation reaction (UOR) owingtoa6e À transfer process,which poses asevere hindrance to their practical use.Herein, taking b-Ni(OH) 2 nanosheets as the proof-of-concept study,wedemonstrated asurface-chemistry strategy to achieve metallic Ni(OH) 2 nanosheets by engineering their electronic structure,r epresenting af irst metallic configuration of transition-metal hydroxides.S urface sulfur incorporation successfully brings synergetic effects of more exposed active sites,good wetting behavior,and effective electron transport, giving rise to greatly enhanced performance for UOR. Metallic nanosheets exhibited amuchhigher current density,smaller onset potential and stronger durability.Driven by growing concerns about global warming and the depletion of fossil fuel, developing renewable energy-production and -storage technologies represent an important but challenging issue. [1][2][3] In this regard, direct urea fuel cells offer great promise for energy-sustainable developments and also mitigating water contamination. [4][5][6] Theu rea fuel cell is designed based on 2CO(NH 2 ) 2 + 3O 2 !2N 2 + 4H 2 O + 2CO 2 , accomplishing power output and concurrently remedying urea-rich wastewater before urea naturally hydrolyzes in the environment. Compared to cathodic oxygen reduction reaction (ORR), the anodic urea oxidation reaction (denoted as UOR, CO(NH 2 ) 2 + 6OH À !N 2 + 5H 2 O + CO 2 + 6e À )undergoes more sluggish kinetics owing to a6e À transfer process and requires the use of electrocatalysts for promoting the reaction rate.T herefore,h igh-performance UOR catalysts are required to reduce the overpotential to drive the sluggish reaction. Although tremendous efforts have been devoted to pursue efficient electrocatalysts to give superior UOR performance, [7][8][9][10][11][12][13][14][15] they still suffer from inferior electrical conductivity and "poisoning", greatly hindering electrochemical efficiency for practical application.Conductive two-dimensional (2D) nanosheets have been explored for high-performance electrocatalysts because of their highly exposed catalytic surface and excellent electron transportation. Tw o-dimensional nanomaterials usually possess exposed surfaces with low-coordinated steps,e dges,a nd kinks,w hich provide abundant active sites to mediate the electrocatalytic process,allowing them to be efficient electrocatalysts. [16] Owing to the dimensionally reduced structure of 2D nanomaterials,i nw hich most of atoms are exposed on surface and thus offer high chemical activity,v arious strategies directed at the surface atoms,including defect engineering, surface incorporation and structural distortion, [17][18][19] have been employed to effectively augment the number of active sites.Moreover,intrinsic high conductivity is also essential fo...

Defective Carbon–CoP Nanoparticles Hybrids with Interfacial Charges Polarization for Efficient Bifunctional Oxygen Electrocatalysis

“…There is no obvious distinction between CoP–DC and CoP bulk, meaning that the existence of the standard CoP framework in both samples. As displayed in the inset of Figure c, a shift of absorption threshold to high energy is observed after the CoP coupled with defective carbon, indicating the electron transfer from the CoP core to defective carbon shell . This result is also consistent with XPS, Co L‐edge, and C K‐edge XANES spectra as discussed above.…”

In Situ Electrochemical Production of Ultrathin Nickel Nanosheets for Hydrogen Evolution Electrocatalysis

“…Urea electrolysis occurred with current densities of 10 mA cm À2 at 1.44 V and 100 mA cm À2 at 1.68 V (Figure S21C), far exceeding the activity of Ni(OH) 2 and also better than the recently reported catalysts. 64,65 The urea electrolysis device also exhibited excellent stability working at 20 mA cm À2 for more than 20 hr (Figure S21D). Moreover, the as-developed approach was applicable to prepare ultrathin NiFe layered double hydroxide with an enhanced OER performance (Figures S22 and S23).…”

Nickel Ferrocyanide as High-Performance Next Generation Electrocatalyst for Urea Oxidation

“…4,6 Compared to OER, UOR suffers from even more sluggish kinetics because of the complicated 6etransfer process, which needs high performance catalysts to decrease the overpotential to achieve an e cient device. 2,[9][10][11] Initially, some noble metal catalysts such as Ti-Pt, Ti-Pt-Ir, and Ru were used to enhance the activity, however due to their scarcity they are costly. 2 However, the catalytic performance of the recently developed non-noble metal UOR catalysts based on Ni hydroxides, oxides, sul des, and phosphides, etc, does not satisfy requirements of practical applications due to the high overpotential, low current density and inadequate stability.…”