【Research Background】
       Single atom catalysts (SACs) have broad application prospects in the field of heterogeneous catalysis. Unlike metal nanoparticles or bulk metal catalysts, SACs are atomically dispersed, isolated, coordination-saturated metal active sites. In addition, they also demonstrate the quantum confinement effect and the metal-skeleton interaction. These unique properties make SACs an ideal catalyst for CO oxidation, oxygen reduction, oxygen generation (OER), hydrogen production (HER), various hydrogen production reactions, CO2 reduction, and other electrochemical applications.

[Introduction]
        Professor H.N. Alshareef of the King Abdullah University of Science and Technology recently published a research paper on MXene-based atomic catalytic hydrogen production in Adv.Mater. Titanium carbide (Ti3C2Tx) MXene is used as an effective solid carrier. The carrier has a ruthenium monoatomic (RuSA) catalyst coordinated by nitrogen (N) and sulfur (S), which has good activity for hydrogen evolution reaction (HER). X-ray absorption, fine structure spectroscopy and scanning transmission electron microscopy showed the atomic distribution of yttrium on Ti3C2Tx MXene carrier and the successful doping of N and S materials on RuSA and Ti3C2Tx MXene. The overpotential of the synthesized RuSA-N-S-Ti3C2Tx catalyst at a current density of 10 mA cm-2 was 76 mV.
       In addition, the study also shows that the integration of RuSA-NS-Ti3C2Tx catalyst on the n+np+-Si photocathode can achieve a very high photocurrent density of 37.6 mAcm−2 for photoelectrochemical hydrogen production, higher than the reported precious metal platinum. Coupling of a noble metal catalyst with a Si photocathode. Density functional theory calculations show that the synergistic relationship between the N and S sites on the RuSA and Ti3C2Tx MXene supports is a source of enhanced activity. This work will expand the possibilities of using the MXene family as a solid support for the rational design of various monoatomic catalysts.

[Graphic introduction]

Figure 1. a) is the flow diagram of RuSA-NS-Ti3C2Tx synthesis b) is the stacking morphology of RuSA-NS-Ti3C2Tx c) the transmission diagram of RuSA-NS-Ti3C2Tx sheet d) is the high resolution transmission diagram of RuSA-NS-Ti3C2Tx It is seen that the presence of the layered MXene e) is a high-angle annular dark field diagram of RuSA-NS-Ti3C2Tx, in which the 钌 single metal atom fg) is characterized by its elemental distribution.

Figure 2. a) Polarization curve for RuSA-NS-Ti3C2Tx and other comparative materials b) tafel curve cd) Polarization curve for RuSA-NS-Ti3C2Tx in 0.5M NaOH and NaSO4 e) EIS impedance test fg) The electric double layer method is used to determine the active area of the material hj) The lateral contrast of the hydrogen production performance of HER.
It can be seen from the polarization curve that RuSA-N-S-Ti3C2Tx has good catalytic activity, low impedance and large active area.

Figure 3. Density functional theory studies: a) atomic model; b) Gibbs hydrogen adsorption free energy; c) density of states.

[Summary of this article]
       The performance of the RuSA-N-S-Ti3C2Tx catalyst is superior to other MXene-based HER catalysts and most transition metal-based HER catalysts reported previously. DFT simulation studies show that the extraordinary catalytic activity of RuSA-N-STi3C2Tx is mainly due to the catalytic interface and the RuSA-Ti3C2Tx MXene framework and its excellent ΔGH* value. In addition, the addition of RuSA-N-S-Ti3C2Tx catalyst to the n+np+-Si photocathode allows the photocurrent density to reach 37.6 mA cm−2, which is 10 times that of the Ti3C2Tx /n+np+-Si photocathode. Both experimental and theoretical studies clearly show that the catalytic properties of MXenes can be adjusted by metal-support interactions. This will have certain guiding significance for the design of MXene-based catalysts in the future.

Literature link:
DOI: 10.1002/adma.201903841

Source: WeChat public account MXene Frontier