Review—The Oxygen Reduction Reaction on MXene-Based Catalysts: Progress and Prospects

Abstract

The oxygen reduction reaction (ORR) is a critical but sluggish reaction used for various applications, including fuel cells and metal-oxygen batteries. Currently, the benchmark catalysts for ORR are Pt-based catalysts. However, due to these catalysts being scarce and very expensive, alternative catalysts that are more abundant and less expensive are urgently in demand. MXenes, a new two-dimensional (2D) material based on transition metal carbides and nitrides, have advanced the performance of various existing applications and technologies, including batteries, supercapacitors, sensors, etc. Owing to their unique electronic structure, physical and chemical properties, and tunable morphology, MXenes are expected to thrive as catalysts in ORR electro- and photo-catalytic systems. Additionally, they are promising catalytic supports for ORR, thus significantly reducing the necessary Pt loading. In this work, we carefully review the most pertinent works on ORR using MXenes. We discuss the gaps and challenges in the field, identify key areas that need further attention, and provide directions for future research.

Sandwich-Structured MXene/Carbon Hybrid Support Decorated with Pt Nanoparticles for Oxygen Reduction Reaction

“…The binding energy of Pt 0 (Table S3) in Pt/MCM (4f 7/2 (71.58 eV), 4f 5/2 (74.83 eV)) are higher than that in Pt/C (4f 7/2 (71.00 eV), 4f 5/2 (74.35 eV)), shows a stronger interaction between Pt NPs and MCM support compared to carbon support. This enhanced interaction can, on the one hand, regulate the electronic structure of Pt NPs, thus accelerating the adsorption/desorption process of reactants and products, and on the other hand, inhibit the dissolution and maturation of Pt NPs, thus imparting improved activity and durability to the Pt/MCM catalyst. , …”

“…With great advances in materials science, coupling Pt nanoparticles with well-designed support, particularly two-dimensional (2D) materials, is another effective way to further improve catalyst performance. − Two-dimensional support not only provides a large number of attachment sites for nanoparticles but also promotes the kinetic of intermediate reactions by modulating the electronic structure of Pt. , MXene is prepared by selective etching of the MAX phase, and its molecular formula is M n +1 X n T x (where M is a transition metal, X is C or N, T is functional groups, e.g., −O, −OH, −F) . As a novel 2D material, MXene, owns a high specific surface area and good hydrophilicity and thus is widely used in the fields of energy, catalysis, and membrane science. − Benefiting from the surface functionalization, active sites can be anchored strongly in the surface of MXene, greatly enhancing the interaction between support and Pt NPs. − However, individual MXene nanosheets as a support are stacked effortlessly, resulting in a significant reduction in specific surface area and catalytic activity .…”

Review and Perspective on Transition Metal Electrocatalysts Toward Carbon-Neutral Energy

“…The high activation potentials is due to the sluggish kinetics of ORR. With regards to MABs and fuel cells in which a more efficient oxygen reduction (i.e., more electrons transferred) is preferred, a catalyst with a 4e – selectivity is ideal. It is worth noting that ORR for noble metals generally follow 4e – whereas carbon-based catalysts undergo 2e – transfer process. , Transition-metal oxides have a different surface charge distribution so, they follow a different ORR mechanism, though the principle is still the same …”

“…The catalyst group M–N–C is comprised of single or heteroatom metal sites (M = Mn, Fe, Co, Ni, etc.) that are coordinated with nitrogen (N) and immobilized on a carbon substrate (C) . M–N–Cs are recognized for their promising catalytic capabilities for ORR and OER, low-cost synthesis procedures, and earth abundance.…”

“…As previously discussed, MXenes possess high electronic conductivity, high specific surface area, hydrophilicity, and tunable size and morphology which make them potential candidates for oxygen catalysis. , However, except for the work of Lin et al on Ti 3 C 2 MXene for ORR, pristine MXenes are not reported for ORR/OER systems . Instead, MXenes function as catalyst supports , – they modulate the electronic density and add more active sites to their cocatalyst . Lei et al synthesized NiCo 2 O 4 /MXene hybrid through an in situ one-pot hydrothermal process .…”