Ultralow Ru Loading Transition Metal Phosphides as High‐Efficient Bifunctional Electrocatalyst for a Solar‐to‐Hydrogen Generation System

Abstract

Water splitting is a promising technology for sustainable conversion of hydrogen energy. The rational design of oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) bifunctional electrocatalysts with superior activity and stability in the same electrolyte is the key to promoting their large‐scale applications. Herein, an ultralow Ru (1.08 wt%) transition metal phosphide on nickel foam (Ru–MnFeP/NF) derived from Prussian blue analogue, that effectively drivies both the OER and the HER in 1 m KOH, is reported. To reach 20 mA cm−2 for OER and 10 mA cm−2 for HER, the Ru–MnFeP/NF electrode only requires overpotentials of 191 and 35 mV, respectively. Such high electrocatalytic activity exceeds most transition metal phosphides for the OER and the HER, and even reaches Pt‐like HER electrocatalytic levels. Accordingly, it significantly accelerates full water splitting at 10 mA cm−2 with 1.470 V, which outperforms that of the integrated RuO2 and Pt/C couple electrode (1.560 V). In addition, the extremely long operational stability (50 h) and the successful demonstration of a solar‐to‐hydrogen generation system through full water splitting provide more flexibility for large‐scale applications of Ru–MnFeP/NF catalysts.

Co-FeS2/CoS2 Heterostructured Nanomaterials for pH Sensing

“…Figure 4 b is the overpotential corresponding to the curve in Figure 4 a after each stability test. It can be seen that after the stability test, the performance only decreased 6 mV, indicating the good reversibility, which is the better reversibility than the previous work [ 12 , 13 , 31 ].…”

“…Due to adsorption/diffusion of H + /OH − ions the surface of nanoflowers becomes charged and it creates an electrical double layer structure by site binding theory. With changes in the pH of a solution the contribution of both H + and OH − ions also varies, which can affect the efficiency of HER [ 13 ]. Also, Figure A1 shows that Co-FeS 2 /CoS 2 nanowires synthesized in previous work were used as a pH sensor, and a similar linear relationship was obtained [ 20 ].…”

“…In renewable energy fields, the electrolysis of water is an important way to produce hydrogen [ 8 , 9 , 10 , 11 ]. Now, non-noble transition metal has been studied in the electrolysis of water [ 12 , 13 , 14 ]. However, the research on using catalyst materials as pH detection sensors, which remains rare.…”

Constructing a Rod‐like CoFeP@Ru Heterostructure with Additive Active Sites for Water Splitting

“…Recently, construction of metal-transition metal phosphides (M/TMPs) interface materials has become significant and attractive. [11][12][13] They can regulate the surface charge densities of catalysts, enhancing the electronic transfer capability and the electron density of activity sites. Among phosphides, one-dimensional (1D) multimetallic phosphides possess outstanding performance due to their abundant active sites and excellent electrical conductivity.…”

Noble Metal Phosphide Electrocatalysts and Their Synchrotron-based X-ray Absorption Spectroscopy

“…11 TEM (a-b), and HRTEM (c) images of Rh2P@NC, polarization curves for Rh2P@NC initial and after 1000 CV scanning and time-dependent current density curve for Rh2P@NC under static overpotential of 20 mV for 10 h (d) [51] , electrocatalytic properties for the HER in 1.0 mol/L KOH of Ru2P/RGO-20, Ru2P and Pt/C (e), free-energy diagram of the HER for RGO, Ru2P,Pt and Ru2P/RGO-20 (f) [81] , band structure of pure RuP2 (left) and RuP2@NPC hybrid (right) (g) [93] , HER polarization curves of the pure metal phosphides and the physical mixture of different metal phosphides and graphene in 0.5 mol/L H2SO4 and 1 mol/L KOH (h) [45] 此外，当磷化物与载体发生耦合作用的同时， 可能会暴露额外的活性位点。 Mu 等 [95] ；贵金属取代过渡金属位置，与磷配位，过渡 金属作为骨架起着稳定结构的作用 [97] 。 Chen 等 [98] 利用水热法在泡沫镍上生长了含有 Ru 前体的 Mn/Fe MOF(MnFe PBA)，低温固相磷化 后得到 Ru 改性的复合催化剂(Ru-MnFeP/NF)，作为 HER、OER 双功能催化剂具有出色的活性与稳定性 (图 12(a))。研究发现 Ru 与磷化物间存在电荷转移， 电子聚集在 Ru 位点，DFT 计算表明 Ru 负载在 Fe2P 或 Mn2P 上时，能有效降低∆GH*(图 12(b))。Li 等 [96] 报道了 Ru 掺杂的 MOF 衍生的 Ru/CoxP@NC 催化剂， 与 CoxP@NC 相比， 前者表现出高效的电催化活性和 对 HER 的长期稳定性。 He 等 [99] 对 NiFe-P 纳米片进行 Ru 掺杂，XPS 结 果表明，由于 Ru 的成功掺杂，Fe2p，Ni2p 和 P2p 的结合能均正向移动，这被认为是提高了电子转移 能力并减少能垒(图 12(c))。同时理论研究证明， Ru 的掺杂不仅提供了新的活性位点(Ru 位点)，而且还 增强了原始位点(P 位点)的活性，从而降低了催化剂 表面对 H *的强烈吸附(图 12(d-f))。 图 12 Ru-MnFeP/NF 催化剂制备示意图(a), Fe2P-Ru h 和 Mn2P-Ru 结构的电荷分布(b) [98] , Ru-NiFe-P 和 NiFe-P 的 XPS 结果(c), Ru-NiFe-P 的吸收模型表面(d), 平衡电势下计算的∆GH*(e), Ru-NiFe-P 和 NiFe-P 的总态密度(f) [99] Fig. 12 Schematic illustration of the fabrication of Ru-MnFeP/NF catalysts (a), calculated charge density differences of Fe2P-Ru and Mn2P-Ru structures (b) [98] , high-resolution XPS spectra of Ni2p, Fe2p and P2p in the Ru-NiFe-P and the NiFe-P (c), the absorption modeled surfaces of Ru-NiFe-P (d), calculated ΔGH* for Ru-NiFe-P, NiFe-P, Ru-Ni-P, Ni-P, Ru-Fe-P and Fe-P (e), total density of states of Ru-NiFe-P and NiFe-P (f) [99] 3 同步辐射 X 射线吸收谱表征 X 射线吸收光谱(XAS)，即 X 射线吸收精细结构 光谱(XAFS)，是利用 X 射线入射前后信号变化来分 析材料元素组成、电子态及微观结构等信息的谱学 手段，对局部原子结构和化学环境敏感 [100] 。XAS 可 分为 X 射线吸收近边结构(X-ray Absorption Near-edge Structure， XANES)和扩展 X 射线精细吸收 结构(Extended X-ray Absorption Fine Structure ， EXAFS)。XANES 对应吸收边前约 10 eV 到边后 50 eV 的区域， EXAFS 对应从吸收边高能侧大约 30 eV 或 50 eV 开始直到边后近 1000 eV 的区域 [101] 。在催 化领域， XAFS 是基于同步辐射的各种表征手段中应 用范围最广泛的一种，在物质结构表征、理化性能 解释等方面发挥着越来越重要的作用。 通过 XANES 可以获得中心原子的氧化态等信 息。对 EXAFS 曲线进行拟合，可以获得中心原子的 配位环境信息，包括周围原子的种类，键长，配位 数和无序度等 [102] 。这些信息对于理解电催化性能至 关重要，并且可以为进一步设计高效的催化剂提供 指导。例如，Guo 等 [103] PdPSA-CN(f)的几何结构, Pd K 边 XANES 光谱(g), EXAFS 在 R(h)和 k(i)空间对应的 k 3 加权傅里叶变换谱 [103] , RuCl3@HPN 和 Ru SAs@PN 的 EXAFS 光谱(j), Ru SAs@PN、 Ru 箔和 RuCl3@HPN 的小波变换谱(k), N 的 K 边(l)、 P 的 L 边(m)NEXAFS 光谱, PN 和 Ru SAs@PN 的质子去耦 31 P 固态 MAS NMR 谱(n) [104]…”