Single-atom catalysts (SACs) especially supported on two-dimensional nitrogen-doped carbon substrate have been widely reported to be able to effectively promote electrocatalytic N₂ reduction reaction (eNRR). The precise design of single-metal-atom active site (SMAS) calls for fundamental understanding of its working mechanism for enhanced eNRR performance. Herein, by means of density functional theory calculations, we theoretically investigate the eNRR performance of nine prototypical SMAS, namely, MN₂B₂ (M: transition metals of IIIB, IVB and VB groups) which comprises of asymmetric ligands of N₂B₂ embedded in defective BN nanosheet. Our results reveal the significant role of spin state of SMAS in tuning the potential-determining steps of eNRR, in which MN₂B₂ site with higher spin magnetic moment (μ) is beneficial to reducing limiting potentials (U_L) of eNRR. Specially, CrN₂B₂ (μ = 4μ_B), VN₂B₂ (μ = 3μ_B) and MoN₂B₂ (μ = 2μ_B) demonstrate high activity and selectivity to eNRR. The asymmetric ligands of N₂B₂ are deemed to be superior over mono-symmetric ligands. More importantly, our results demonstrate that breaking (or deviating) of the scaling relations between key N-containing intermediates (*N₂H/*N₂ and *NH₂/*N₂) on MN₂B₂ can be realized by enhancing spin state of SMAS which renders the active site a balanced N-affinity critical for efficient eNRR. This observation is validated by the calculated Sabatier volcano-shape relation between eNRR limiting potentials and N₂ adsorption energy. Our study develops the guidance for catalyst design to boost eNRR performance by tuning the spin state of an active site.

特别是负载在二维氮掺杂碳基底上的单原子催化剂 (SAC) 已被广泛报道能够有效地促进电催化N ₂还原反应 (eNRR)。单金属原子活性位点 (SMAS) 的精确设计要求对其工作机制有基本的了解，以提高 eNRR 性能。在此，我们通过密度泛函理论计算，从理论上研究了 9 种原型 SMAS 的 eNRR 性能，即由 N ₂ B ₂的不对称配体组成的MN ₂ B ₂（M：IIIB、IVB 和 VB 基团的过渡金属）嵌入有缺陷的 BN 纳米片中。我们的研究结果揭示SMAS的自旋态的在调谐eNRR的电位确定步骤的显著作用，其中MN ₂乙₂部位具有更高的自旋磁矩（μ）是减少限制性电位（有益û_大号eNRR的）。特别地，CrN ₂ B ₂ ( μ = 4 μ _B )、VN ₂ B ₂ ( μ = 3 μ _B ) 和 MoN ₂ B ₂ ( μ = 2 μ _{B )}) 表现出对 eNRR 的高活性和选择性。N ₂ B ₂的不对称配体被认为优于单对称配体。更重要的是，我们的结果表明，可以通过增强MN ₂ B ₂上的关键含 N 中间体（*N ₂ H/*N ₂和 *NH ₂ /*N ₂）之间的缩放关系来打破（或偏离）SMAS 的自旋状态，这使活性位点具有平衡的 N 亲和性，这对于有效的 eNRR 至关重要。这一观察结果得到了 eNRR 极限电位和 N ₂之间计算的萨巴蒂尔火山形状关系的验证吸附能。我们的研究为催化剂设计提供了指导，通过调整活性位点的自旋状态来提高 eNRR 性能。