The poly(heptazine imide) (also known as heptazine-based crystalline carbon nitride, abbreviated as PHI) has drawn wide attention in solar energy conversion, which is profited from its improved photoinduced charge separation compared with melon-based carbon nitride. Nevertheless, the crystallinity of the samples synthesized by direct heat-treating precursors is low and further impede electron transport. This situation is especially prominent if precursors are used in large quantities and the reason is also unclear at present. Herein, this crucial issue was preliminarily revealed: the by-product HCl formed in the synthesis process has seriously restricted the deamination of PHI if it cannot be removed in time. Based on this, an original alkali-assisted method was proposed and demonstrated to realize deep-deamination for improving the crystallinity and extending π-conjugation of PHI. Benefit from this, alkali-assisted synthesized PHI illustrates significantly enhanced electron transport performance and further improved photocatalytic H₂ evolution activity. The optimized PHI exhibits highly boosted photocatalytic H₂ evolution activity of 2223 μmol h⁻¹, which is 18 times that of original PHI synthesized without alkali-assistance. Additionally, the mechanism was further verified by density-functional theory (DFT) computations and the universality of alkali-assisted method was verified by using different kinds of alkali.

聚（庚嗪酰亚胺）（也称为庚嗪基结晶碳氮化物，缩写为 PHI）在太阳能转换中引起了广泛关注，这得益于其与瓜基氮化碳相比改进的光致电荷分离。然而，通过直接热处理前体合成的样品的结晶度较低，进一步阻碍了电子传输。如果前体大量使用，这种情况尤为突出，目前原因也不清楚。在此，初步揭示了这一关键问题：合成过程中形成的副产物HCl若不能及时去除，将严重制约PHI的脱氨。基于此，提出并论证了一种新颖的碱辅助方法来实现深度脱氨，以提高 PHI 的结晶度和延长 π-共轭。受益于此，碱辅助合成的 PHI 说明了显着增强的电子传输性能和进一步改善的光催化 H₂进化活动。优化后的 PHI 表现出2223 μmol h ^{−1的高度提升的光催化 H} ₂释放活性，是没有碱辅助合成的原始 PHI 的 18 倍。此外，通过密度泛函理论（DFT）计算进一步验证了该机理，并通过使用不同种类的碱验证了碱辅助方法的普适性。