Realizing multiferroics in α-Ga2S3via hole doping: a first-principles study.

Using first-principles calculations, we report the realization of multiferroics in an intrinsic ferroelectric α-Ga2S3 monolayer. Our results show that the presence of intrinsic gallium vacancies, which is the origin of native p-type conductivity, can simultaneously introduce a ferromagnetic ground state and a spontaneous out-of-plane polarization. However, the high switching barrier and thermodynamic irreversibility of the ferroelectric reversal path disable the maintenance of ferroelectricity, suggesting that the defect-free form should be a prerequisite for Ga2S3 to be multiferroic. Through applying strain, the behavior of spontaneous polarization of the pristine α-Ga2S3 monolayer can be effectively regulated, but the non-magnetic ground state does not change. Strikingly, via an appropriate concentration of hole doping, stable ferromagnetism with a high Curie temperature and robust ferroelectricity can be concurrently introduced in the α-Ga2S3 monolayer. Our work provides a feasible method for designing 2D multiferroics with great potential in future device applications.

Precise Engineering of the Electrocatalytic Activity of FeN4-Embedded Graphene on Oxygen Electrode Reactions by Attaching Electrides.

Using first-principles calculations combined with a constant-potential implicit solvent model, we comprehensively studied the activity of oxygen electrode reactions catalyzed by electride-supported FeN4-embedded graphene (FeN4Cx). The physical quantities in FeN4Cx/electrides, i.e., work function of electrides, interlayer spacing, stability of heterostructures, charge transferred to Fe, d-band center of Fe, and adsorption free energy of O, are highly intercorrelated, resulting in activity being fully expressed by the nature of the electrides themselves, thereby achieving a precise modulation in activity by selecting different electrides. Strikingly, the FeN4PDCx/Ca2N and FeN4PDCx/Y2C systems maintain a high oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) activity with the overpotential less than 0.46 and 0.62 V in a wide pH range. This work provides an effective strategy for the rational design of efficient bifunctional catalysts as well as a model system with a simple activity-descriptor, helping to realize significant advances in energy devices.

TM2 -B2 Quadruple Active Sites Supported on a Defective C3 N Monolayer as Catalyst for the Electrochemical CO2 Reduction: A Theoretical Perspective.

Developing high-performance electrocatalysts for the CO2 reduction reaction (CO2 RR) holds great potential to mitigate the depletion of fossil feedstocks and abate the emission of CO2 . In this contribution, using density functional theory calculations, we systematically investigated the CO2 RR performance catalyzed by TM2 -B2 (TM=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu) supported on a defective C3 N monolayer (V-C3 N). Through the screening in terms of stability of catalyst, activity towards CO2 adsorption, and selectivity against hydrogen evolution reaction, Mn2 -, Fe2 -, Co2 -, and Ni2 -B2 @V-C3 N were demonstrated to be a highly promising CO2 RR electrocatalyst. Due to quadruple active sites, these candidates can adsorb two or three CO2 molecules. Strikingly, different products, distributing from C1 to C2+ , can be generated. The high activity originates from the synergistic effect of TM and B atoms, in which they serve as adsorption sites for the C- and O-species, respectively. The high selectivity towards C2+ products at the Fe2 -, and Ni2 -B2 sites stems from moderate C adsorption strength but relatively weak O adsorption strength, in which a universal descriptor, that is, 0.6 ΔEC -0.4 ΔEO =-1.77 eV (ΔEC /ΔEO is the adsorption energy of C/O), was proposed. This work would offer a novel perspective for the design of high active electrocatalysts towards CO2 RR and for the synthesis of C2+ compounds.

Enhancement of Interfacial Charge Transfer of TiO2/Graphene with Doped Ca2+ for Improving Electrical Conductivity.

Imparting surface coatings with conductivity is an effective way to prevent fire and explosion caused by electrostatic discharge. TiO2 is a commonly used paint; however, intrinsic TiO2 has poor electrical conductivity. Herein, we develop a method to make TiO2 coating highly conductive by doping Ca2+ into the TiO2 lattice based on the introduction of graphene. It is demonstrated that doping Ca2+ increases the carrier density of TiO2 and its morphology changes from a sphere to a spindle shape, which increases the interfacial contact area between TiO2 and graphene. Therefore, resistivity can be greatly decreased due to the construction of fast charge transport pathways from TiO2 to graphene, resulting from an increase in the speed of interfacial charge transfer. In addition, the electronic properties of the samples are also studied through first-principles calculations before and after Ca2+ doping. The result of the theoretical analysis is in agreement with that of experiments. Thus, the lowest resistivity of Ca2+-TiO2/graphene can reach 0.004 Ω cm. Consequently, the feature of superior conductivity of the Ca2+-TiO2/graphene composite endows it with practical application potential in the field of antistatic coating.