Nickel‐Doped Carbon Dots as an Efficient and Stable Electrocatalyst for Urea Oxidation

Abstract

Urea is a typical contaminant present in wastewater which may cause severe environmental problems. Electrochemical catalytic oxidation of urea has emerged as an efficient approach to solve this problem. Nevertheless, the current nickel‐based catalysts (e.g., nickel hydroxide/sulfides) feature a high metal content. It not only lowers the utilization efficiency of nickel but also causes secondary pollution to the environment. Here, nickel‐doped carbon dots (Ni‐CDs) with an excellent and stable catalytic activity for the electrocatalytic urea oxidation reaction (UOR) are reported. Specifically, carbon dots (CDs) with abundant functional groups are synthesized by a one‐pot hydrothermal method and then Ni‐CDs with a very low metal content (1.1 at%) are prepared. The Ni2+ sites by coordination with carboxylic groups on the CDs provide excellent electrocatalytic activity and excellent durability for the UOR, as demonstrated by an anodic current density of 100 mA cm−2 at a potential of 1.38 V (vs RHE) and similar experimental results in practical application. To the best of knowledge, this is the first report of CDs‐based materials applied for the UOR, which opens an important new area of applicability for CDs as well as broadens the scope of the materials for electrochemical catalysis of urea.

The Guidelines for the Design and Synthesis of Transition Metal Atom Doped Carbon Dots

“…However, not all TMAs can serve as dopants for preparing TMAs‐doped CDs. Currently, most research efforts are focused on atoms such as Mn, [16,23] Fe, [21] Co, [30,32] Ni, [27,33] Cu, [19,34] and Zn [35] . Understanding the properties of these TMAs is necessary to design TMAs‐doped CDs with specific functions accurately.…”

“…[25] Benefiting from the co-doping of Gd and Yb, Gd, Yb-CDs achieved MRI and computed tomography imaging (CTI) capabilities (Figure 2d). Besides, o-phenylenediamine (OPD), [26] urea, [27] and guanidine hydrochloride, [28] which are small amino-rich molecules, can also be used as electron donors for TMAs to synthesize TMAs-doped CDs. It is worth noting that using multiple ligands in combination to anchor TMAs demonstrates the flexibility in the design and synthesis of TMAs-doped CDs, making it the most effective strategy for preparing TMAs-doped CDs at present.…”

Supramolecular Surface Engineering of Carbon Dots Enables Matrix‐Free Room Temperature Phosphorescence†

“…[ 7‐11 ] CDs have been widely used in sensing, in vitro / in vivo imaging, cancer therapy, catalysts and optoelectronic devices. [ 12‐19 ] Despite the well documented fluorescent properties, CDs with RTP have also been reported by several groups. [ 20 ] Lin and co‐workers reported the production of effective RTP by aggregation‐induced of CDs in trimellitic acid.…”

Water‐Stable Fluorous Metal–Organic Frameworks with Open Metal Sites and Amine Groups for Efficient Urea Electrocatalytic Oxidation

“…[5][6][7] Besides, one of the priorities in the quality improvement of drinking water is urea removal, presenting an opportunity for Urea oxidation reaction (UOR) UOR [8] and proposing a sustainable procedure to control pollutants and harvest energy. Electrochemical oxidation is among the effective strategies used to convert urea and treat wastewater, [9][10][11] producing energy or generating electricity from urea-rich wastewater by a direct urea fuel cell and providing the high potential to simultaneously treat water and recover energy. [12][13][14][15] Urea complete oxidation for the N 2 and CO 2 generation requires 6 successive proton-coupled electron transfer steps based on the electrode halfreactions below in the presence of OH − groups: CO(NH 2 ) 2(aq) + 6OH − (aq) → N 2(g) + 5H 2 O (aq) + CO 2(g) + 6e − .…”