First-Principles Insight into the Mechanistic Study of Electrochemical Cyanide Reduction Reaction on Post-Transition Metal Based Single-Atom Catalysts Anchored by Phthalocyanine Nanosheets

As a catalytic center, the 4N-coordinated post-transition metal (PM) confined within phthalocyanine (Pc) shows promise for the environmentally friendly synthesis of CH4 and NH3. A range of PM–Pc catalysts (where PM represents Al, Ga, In, Tl, Ge, Sn, Pb, and Bi) is methodically evaluated through DFT mechanistic analysis and electrochemical exploration to determine their stability, activity, and selectivity. Our comparative analysis reveals that the orientational specificity of initial cyanide adsorption would play a crucial role in cyanide electroreduction reaction (CNRR) pathways within diverse PM–Pc nanosheets. Specifically, the NC* model typically requires higher supplies of Gibbs free energy for the CNRR, preponderantly resulting in CH3NH2. Conversely, the counterpart of the CN* model necessitates lower energetic demands, leading to a broader diversity of products including methane and ammonia. Of particular significance that the relationships of limiting potentials (UL) through two types of descriptors, ΔGNC*→HNC* and ΔGCN*→HCN*, were essential for constructing volcano plots, thus illustrating the relation within the intrinsic adsorption performance of diverse PM–Pc series and their associated prominent CNRR efficiency. From a comprehensive screening of the studied results, we have determined that the nanosheets Al–Pc, In–Pc, Ge–Pc, and Sn–Pc (triggered by the CN* model) are the exceptionally proficient electrocatalysts, specifically in producing only CH4 and NH3 via the CNRR process, as indicated by our final compiled findings. Within the range of nanosheets evaluated, the Al–Pc associated model emerges as a standout, demonstrating markedly higher selectivity and CNRR activity than its counterparts. This study advances the understanding of the unique superior characteristics of SACs, subsequently providing innovative perspectives that could directly guide their discovery for CNRR applications.