Symmetry breaking of single-atom catalysts in heterogeneous electrocatalysis: reactivity and configuration

Single-atom catalysts (SACs) have emerged as transformative materials in heterogeneous electrocatalysis, yet their conventional symmetric coordination environments often yield suboptimal catalytic efficacy. This review systematically examines the deliberate disruption of local symmetry as a powerful design strategy to precisely tailor the electronic properties of SACs. We categorize and analyze atomic-level modulation approaches, including strain-induced lattice distortion, defect-engineered coordination tailoring, and curvature-derived interfacial fields, demonstrating how these strategies effectively break the intrinsic symmetry of motifs such as M-N₄. Our analysis reveals that such symmetry breaking redistributes electron density around the metal center, lifts orbital degeneracy, and optimizes the d-band center, leading to enhanced intermediate adsorption, accelerated reaction kinetics, and broken scaling relationships. Furthermore, these asymmetrically configured SACs exhibit improved stability through strengthened metal-support interactions. While significant progress has been made, we conclude that future efforts must address the challenges of atomic-level precision, stability under operation, and scalable synthesis to fully realize the potential of symmetry-broken SACs across various electrocatalytic applications, thereby establishing a new paradigm for the rational design of advanced electrocatalytic materials.