陈俊翔/叶金花/刘乐全ACS Catal.:光催化全解水析氢助催化剂—Ni包覆N掺杂石墨烯层

助催化剂在光催化全解水(POWS)中具有重要意义。镍基共催化剂是替代Pt等代表性贵金属的有吸引力的候选催化剂，但其稳定性差，效率低。在本研究中，包裹在氮掺杂超薄石墨烯(NC)层中的Ni纳米颗粒被证明是一种活性、稳定和低成本的POWS助催化剂。结果表明:Ni@NC/SrTiO₃(STO)的析氢速率约为Ni/STO的3.2倍，甚至优于典型Pt助催化剂。实验和XPS研究表明，氮掺杂石墨烯的选择性涂层有效地抑制了Ni在反应过程中的不利氧化。除了载流子动力学的改善外，动力学研究表明，引入N后，POWS的表观活化能降低了44%。借助机器学习势，进行了深入的理论研究，通过对每个模型结构上约700个位点进行单点能量计算，统计明确了具有合适H*吸附的活性位点。理论计算表明，N掺杂对石墨烯电子结构的修饰显著促进了高自旋密度活性位点的分布。这项工作证明了使用高稳定性和高活性的镍基光催化剂用于全解水的巨大潜力。

Figure 1. Structure of Ni@NC/STO. (a) XRD patterns of STO, Ni/STO, Ni@C/STO, and Ni@NC/STO; (b) SEM image of Ni@NC/STO; (c) TEM image of Ni@NC/STO (inset: the statistic analysis of the Ni NP size distribution); (d) HRTEM image of Ni@NC/STO; (e) HRTEM image of Ni@2NC/STO; and (f) HRTEM image of Ni@4NC/STO.

Figure 2. Light absorption and shell structure characterizations. (a) Ultraviolet−visible (UV−vis) diffuse reflectance spectra of Ni/STO, Ni@C/ STO, and Ni@NC/STO; (b) Raman spectra of Ni@C/STO and Ni@NC/STO; (c) XPS C 1s spectrum of Ni@NC/STO; and (d) XPS N 1s spectrum of Ni@NC/STO.

Figure 3. Catalytic performance and backward reaction. (a) Gas evolution during the overall water splitting reaction of Ni/STO, Ni@C/STO, and Ni@NC/STO over 5 h (the solid and dashed lines represent H2 and O2, respectively); (b) rates of the gas evolution of hydrogen and oxygen for the Ni@NC/STO and Pt/STO overall water splitting reactions for 1 h; (c) time course of POWS under irradiation for 7 h and under darkness for 3 h using Ni@NC/STO and Pt/STO (the solid and dashed lines represents H2 and O2, respectively); and (d) cyclic stability test of Ni@NC/STO. Reaction conditions: 50 mg of catalyst, 100 mL of deionized water, and a 300 W Xe lamp.

Figure 4. Changing of the chemical state on POWS and the effect on activity. (a) XPS Ni 2p3/2 spectra of Ni/STO and used Ni/STO after a 5 h POWS test; (b) XPS Ni 2p3/2 spectrum of NiO/STO; (c) gas evolution during the overall water splitting reaction of Ni/STO, NiO/STO, and STO; and (d) XPS Ni 2p3/2 spectrum of Ni@NC/STO.

Figure 5. Study of the carrier dynamics. (a) Steady-state PL spectra of Ni/STO, Ni@C/STO, and Ni@NC/STO; (b) time-resolved PL decay spectra of Ni/STO, Ni@C/STO, and Ni@NC/STO; and (c) EIS Nyquist plots and (d) transient photoelectric current responses of Ni/STO, Ni@C/STO, and Ni@NC/STO.

Figure 6. Photocatalytic reactions and the kinetic study. (a) Photocatalytic HER (left) and photocatalytic OER (right) rates in 1 h of Ni/STO, Ni@C/STO, and Ni@NC/STO, tested with methanol and silver nitrate as the sacrificial agents, respectively, and (b) the apparent activation energy for the POWS of Ni/STO, Ni@C/STO, and Ni@NC/STO.

Figure 7. DFT calculations. (a) Models of C/STO, Ni@C/STO, Ni@NC/STO, and Ni/STO used for DFT calculations. Green: Ni, red: O, pink: Sr, gray: Ti, brown: C, and blue: N. Red and blue represent active sites and sample sites, respectively. (b) The ratio of active sites for the photocatalytic HER (PC-HER) of Ni/STO, Ni@NC/STO, Ni@C/STO, and C/STO. (c) The competitive adsorption of O* and OH* on Ni/STO. (d) The competitive adsorption of O* and OH* on Ni@NC/STO. (e) The distribution of H* adsorption energy of Ni@C/STO, Ni@NC/STO, and C/STO. (f) The radial distribution function of effective active sites for N (the average site is the average of the radial distributionfunction of all sites).

Ni Coated with N‑doped Graphene Layer as Active and Stable H2 Evolution Cocatalysts for Photocatalytic Overall Water Splitting

https://doi.org/10.1021/acscatal.3c03405