Electroreduction of CO2 with Tunable Selectivity on Au-Pd Bimetallic Catalyst: A First Principle Study

Improvement in Oxygen Evolution Performance of NiFe Layered Double Hydroxide Grown in the Presence of 1T-Rich MoS2

NiFe layered double hydroxide (NiFe LDH) grown in the presence of MoS₂ (rich in 1T phase) shows exceptional performance metrics for alkaline oxygen evolution reaction (OER) in this class of composites. The as-prepared NiFe LDH/MoS₂ composite (abbreviated as MNF) exhibits a low overpotential (η₁₀) of 190 mV; a low Tafel slope of 31 mV dec^-1; and more importantly, a high stability in its performance manifested by the delivery of current output for 45 h. It is important to note that this could be achieved with an exceedingly low loading of 0.14 mg cm^-2. The mass activity of this composite (97 A g^-1) is about 14 times greater than that of the conventional RuO₂ (7 A g^-1) at η = 200 mV. When normalized with respect to the total metal content, a mass activity of 1000 A g^-1 (η = 300 mV) was achieved. Impedance analysis further reveals that the significant reduction in charge-transfer resistance and hence high current density (5 times greater as compared to NiFe LDH at η = 300 mV) observed for MNF is associated with interfacial adsorption kinetics of intermediates (R₁). Significant enhancement in the intrinsic activity of MNF over LDH has been observed through normalization of current with the electrochemically active surface area. Computational studies suggest that the Ni centers in the composite act as the active sites for OER, which is well-corroborated with the observed postreaction appearance of Ni³⁺ species.

Why heterogeneous single-atom catalysts preferentially produce CO in the electrochemical CO2 reduction reaction

Formate and CO are competing products in the two-electron CO2 reduction reaction (2e CO2RR), and they are produced via *OCHO and *COOH intermediates, respectively. However, the factors governing CO/formate selectivity remain elusive, especially for metal-carbon-nitrogen (M-N-C) single-atom catalysts (SACs), most of which produce CO as their main product. Herein, we show computationally that the selectivity of M-N-C SACs is intrinsically associated with the CO2 adsorption mode by using bismuth (Bi) nanosheets and the Bi-N-C SAC as model catalysts. According to our results, the Bi-N-C SAC exhibits a strong thermodynamic preference toward *OCHO, but under working potentials, CO2 is preferentially chemisorbed first due to a charge accumulation effect, and subsequent protonation of chemisorbed CO2 to *COOH is kinetically much more favorable than formation of *OCHO. Consequently, the Bi-N-C SAC preferentially produces CO rather than formate. In contrast, the physisorption preference of CO2 on Bi nanosheets contributes to high formate selectivity. Remarkably, this CO2 adsorption-based mechanism also applies to other typical M-N-C SACs. This work not only resolves a long-standing puzzle in M-N-C SACs, but also presents simple, solid criteria (i.e., CO2 adsorption modes) for indicating CO/formate selectivity, which help strategic development of high-performance CO2RR catalysts.