Core–Shell Structured MXene@Carbon Nanodots as Bifunctional Catalysts for Solar-Assisted Water Splitting

Abstract

The design of nonprecious bifunctional electrocatalysts with high activity and prolonged durability in a wide pH range is essential for the development of the highly efficient, cost-effective, and simplified overall water splitting systems. Here, we report core–shell structured MXene@carbon (MX@C) nanodot hybrids with high bifunctional activity, where N-doped carbon shells are grown in a heteroepitaxial manner strongly interacting with the MXene core. The resulting MX@C nanodot hybrids show enhanced catalytic activity for electrochemical hydrogen evolution reaction (HER) in various pH media from 0 to 14. At pH 14, MX@C achieves the low onset potential of 134 mV at 10 mA/cm2 and reduced Tafel slope of 32 mV/dec due to the facilitated charge transfer along the recombination reaction. For the oxygen evolution reaction (OER), MX@C nanodots are incorporated onto the surface of molybdenum-doped bismuth vanadate (Mo:BiVO4) as a cocatalyst of the photoanode, thereby achieving 1.5 times higher photocurrent density than pristine Mo:BiVO4 at 1.23 V (vs reversible hydrogen electrode) due to the enhanced light absorption and charge transfer efficiency. The superiority of this hybrid catalyst is demonstrated implementing the solar-assisted overall water splitting cells based on the MX@C cathode and MX@C/Mo:BiVO4 photoanode. These cells show the enhancement of current density from 0.78 to 1.23 mA/cm2 with long-term durability over 8 h. These results are attributed to the facile surface catalytic kinetics of the chemically and electronically coupled MX@C hybrid at the heterointerface for both OER and HER.

MXene‐Copper/Cobalt Hybrids via Lewis Acidic Molten Salts Etching for High Performance Symmetric Supercapacitors

“…The general formula is M n +1 X n T y ( n =1–3), where M is early d‐block transition metals, X refers to C and/or N, and T stands for surficial functional groups depending on synthetic procedure and post‐synthetic processing [3] . MXenes show great promise in extensive applications, such as energy storage and conversion, [4–6] water purification, [7] catalysts, [8] due to their 2D layered structure, metallic conductivity, and hydrophilic surfaces [9] …”

MXene‐Copper/Cobalt Hybrids via Lewis Acidic Molten Salts Etching for High Performance Symmetric Supercapacitors

“…[1,2] The general formula is M n+1 X n T y (n = 1-3), where M is early d-block transition metals, X refers to C and/or N, and T stands for surficial functional groups depending on synthetic procedure and postsynthetic processing. [3] MXenes show great promise in extensive applications, such as energy storage and conversion, [4][5][6] water purification, [7] catalysts, [8] due to their 2D layered structure, metallic conductivity, and hydrophilic surfaces. [9] Owing to the high specific surface areas and the confinement of electrons within ultrathin region, 2D nanomaterials become one of the best candidates to achieve high-performance supercapacitors.…”

Electronically coupled layered double hydroxide/MXene quantum dot metallic hybrids for high‐performance flexible zinc–air batteries

“…As illustrated in Figure 1(A), the LDH/MQD/NG hybrids were synthesized by urea‐assisted co‐precipitation of Ni 2+ and Fe 2+ in the presence of MQDs and NG. First, MQDs were prepared by the top‐down conversion of MXene, as previously reported 34 . The UV–visible spectrum of the MQDs shows an clear absorption peak at 262 nm, with a tail extending to the visible range (Figure S1a).…”

“…Owing to their hydrophilic surface and metallic conductivity, 2D MXenes can modify the properties of LDH‐based materials 29–32 . Moreover, the transformation of 2D MXene into 0D MXene quantum dots (MQDs) provides new functionality and modulates the electronic properties owing to the quantum confinement effect and surface‐terminated functional groups in the latter 33,34 . Therefore, the chemical coupling of NiFe‐LDH with MQDs has been proposed an approach for modulating the electronic structure and improving the electrocatalytic properties of NiFe‐LDH.…”