Sugawara Yuuki, Nakase Yuto, Anilkumar Gopinathan M, Kamata Keigo, Yamaguchi Takeo
Laboratory for Chemistry and Life Science, Institute of Integrated Research, Institute of Science Tokyo Yokohama Kanagawa 226-8501 Japan
R&D Centre, Noritake Co., Ltd Miyoshi Aichi 470-0293 Japan.
Nanoscale Adv. 2024 Dec 9;7(2):456-466. doi: 10.1039/d4na00794h. eCollection 2025 Jan 14.
Metal phosphate-type compounds have been utilized in diverse applications, and their distinctive chemical properties have recently opened avenues for their use as catalysts. Metal phosphates have previously demonstrated significant electrocatalytic activity for the anodic oxygen evolution reaction (OER) in electrochemical water splitting. However, the critical factors influencing OER electrocatalysis on Ni-based phosphates have been insufficiently explored. We herein demonstrate nickel (Ni)-based phosphates-monoclinic Ni(PO), monoclinic NiPO, and monoclinic NiPO-as exemplary materials exhibiting outstanding OER activity in alkaline media. These Ni-based phosphates exhibit superior OER overpotentials compared to conventional Ni-based oxides (NiO) and phosphides (NiP). Additionally, their OER-specific activity surpasses that of the rare metal-based benchmark, IrO, and previously reported state-of-the-art crystalline electrocatalysts comprising nonprecious metals. Long-term durability tests show that Ni(PO) maintains its OER activity even after 1000 repeated potential cycles while retaining its elemental composition and Raman spectrum. To understand the excellent OER activities of Ni-based phosphates, the atomic configurations within their crystals are examined. Remarkably, a clear correlation between Ni-O bond length and OER overpotentials is observed in both Ni-based phosphates and NiO, , shorter Ni-O bond lengths are highly beneficial for the OER. Density functional theory (DFT) calculations revealed that the outstanding OER activities of Ni-based phosphates are facilitated by their favorable electronic orbitals, which strengthen the Ni-O bond and improve the adsorption of OER intermediates on Ni sites. This mechanism is substantiated by DFT calculations employing surface slab models, where the adsorption of OER intermediates on the surface of Ni-based phosphates is more energetically favorable than on the surface of NiO. Hence, Ni-based phosphates are promising OER electrocatalysts, and this study provides important guidelines to further improve Ni-based electrocatalysts.
金属磷酸盐类化合物已被应用于各种不同的领域，其独特的化学性质最近为它们作为催化剂的应用开辟了道路。金属磷酸盐此前已在电化学水分解中对阳极析氧反应（OER）表现出显著的电催化活性。然而，影响镍基磷酸盐OER电催化的关键因素尚未得到充分研究。我们在此展示了镍（Ni）基磷酸盐——单斜晶系的Ni(PO)、单斜晶系的NiPO和单斜晶系的NiPO——作为在碱性介质中表现出出色OER活性的典型材料。与传统的镍基氧化物（NiO）和磷化物（NiP）相比，这些镍基磷酸盐表现出优异的OER过电位。此外，它们的OER比活性超过了稀有金属基基准材料IrO以及先前报道的包括非贵金属的最先进的晶体电催化剂。长期耐久性测试表明，即使经过1000次重复的电位循环，Ni(PO)仍能保持其OER活性，同时保持其元素组成和拉曼光谱。为了理解镍基磷酸盐优异的OER活性，对其晶体中的原子构型进行了研究。值得注意的是，在镍基磷酸盐和NiO中都观察到Ni-O键长度与OER过电位之间存在明显的相关性，较短的Ni-O键长度对OER非常有利。密度泛函理论（DFT）计算表明，镍基磷酸盐优异的OER活性得益于其有利的电子轨道，这些轨道加强了Ni-O键并改善了OER中间体在Ni位点上的吸附。采用表面平板模型的DFT计算证实了这一机制，其中OER中间体在镍基磷酸盐表面的吸附在能量上比在NiO表面更有利。因此，镍基磷酸盐是很有前景的OER电催化剂，这项研究为进一步改进镍基电催化剂提供了重要指导。
