Experimental and Computational Insights into the Overall Water Splitting Reaction by the Fe–Co–Ni–P Electrocatalyst

Abstract

Nonprecious transition-metal phosphides (TMPs) are versatile materials with tunable electronic and structural properties that could be promising as catalysts for energy conversion applications. Despite the facts, TMPs are not explored thoroughly to understand the chemistry behind their rich catalytic properties for the water splitting reaction. Herein, spiky ball-shaped monodispersed TMP nanoparticles composed of Fe, Co, and Ni are developed and used as efficient electrocatalysts for hydrogen and oxygen evolution reaction (HER, OER), and overall water splitting in alkaline medium; and their surface chemistry was explored to understand the reaction mechanism. The optimized Fe 0.5 CoNi 0.5 P catalyst shows attractive activities of HER and OER with low overpotentials and Tafel slopes, and with high mass activities, turnover frequencies, and exchange current densities. When applied to overall water splitting, the electrolyzer Fe 0.5 CoNi 0.5 P||Fe 0.5 CoNi 0.5 P cell can reach a 10 mA cm −2 current density at cell voltages of only 1.52 and 1.56 V in 1.0 M and 30 wt % KOH, respectively, much lower than those of commercial IrO 2 ||Pt/C. The optimized electrolyzer with sizable numbers of chemically active sites exhibits superior durability up to 70 h and 5000 cycles in 1.0 M KOH and can attain a current density as high as 1000 mA cm −2 , showing a class of efficient bifunctional electrocatalysis. Experimental and density functional theory-based mechanistic analyses reveal that surface reconstruction takes place in the presence of KOH to form the TMP precatalyst, which results in high coverage of oxygen active species for the OER with a low apparent activation energy (E a ) for conversion of *OOH to O 2 . These also evidenced the thermoneutral adsorption of H* for the efficient HER half-reaction.

Exfoliated Cobalt-Doped Manganese Oxide Nanosheets: An Efficient and Stable Electrocatalyst for Hydrogen Evolution Reaction in an Alkaline Medium

“…Plotting of the ratio of the overpotential (η 10 ) of x = 0.2 to others (i.e., x = 0.0, 0.3, 0.4, and 0.5) and the ratio of the BET surface area of x = 0.0, 0.3, 0.4, and 0.5 to x = 0.2 Co-doped MnO 2 NSs vs different degrees (i.e., x ) of Co-doped MnO 2 NSs reveals close corroborative results as shown in Figure c. Therefore, we may infer that the BET surface area and ECSA greatly influence the electrochemical HER performance Low R ct and high j 0 It is well-putative that materials with higher electrical conductivity, low charge transport resistance ( R ct ), and high exchange current density ( j 0 ) play a vital role toward HER activity.…”

“…Plotting of the ratio of the overpotential (η 10 ) of x = 0.2 to others (i.e., x = 0.0, 0.3, 0.4, and 0.5) and the ratio of the BET surface area of x = 0.0, 0.3, 0.4, and 0.5 to x = 0.2 Co-doped MnO 2 NSs vs different degrees (i.e., x ) of Co-doped MnO 2 NSs reveals close corroborative results as shown in Figure c. Therefore, we may infer that the BET surface area and ECSA greatly influence the electrochemical HER performance …”

“…The accurate measurement of catalytically active site density is quite tough for most solid-state catalysts as not all of the surface atoms are catalytically active or equally accessible but still offers a yardstick for comparing the catalytic activities among various catalysts, especially within a similar system. , The ECSA was assessed via cyclic voltammetry (CV) in the non-Faradaic region under the same conditions used for catalysis measurements but at different scan rates. All samples exhibited similar CV plots (Figure d and Figure S7a–d) under different scan rates, indicating good reversibility . The differences between charge/discharge current density (| Δj |) vs scan rates ( v ) are plotted (Figure e) for all the compositions, and a straight-line relationship was obtained.…”

“…All samples exhibited similar CV plots (Figure 6d and Figure S7a−d) under different scan rates, indicating good reversibility. 66 The differences between charge/discharge current density (|Δj|) vs scan rates (v) are plotted (Figure 6e) for all the compositions, and a straight-line relationship was obtained. The slope (m), which is twice the double-layer capacitance density (C dl ), was found to be 0.244 μF cm −2 for x = 0.2, which is maximum among all other compositions (x = 0.0|m = 0.169 μF cm −2 , x = 0.3|m = 0.195 μF cm −2 , x = 0.4|m = 0.213 μF cm −2 , and x = 0.5|m = 0.192 μF cm −2 ).…”

Constructing Chainmail-Structured CoP/C Nanospheres as Highly Active Anodic Electrocatalysts for Oxygen Evolution Reaction

“…On the other hand, enhancing their stability of CoP catalysts, especially the solubility resistance, is also crucial. Morphology control of CoP, such as the construction of nanowires, , nanospheres, − and nanotubes, , is one key method to improve the durability of catalysts. Compared with all the nanostructures, the core–shell structure is an effective way to prevent internal metal dissolution. − Besides, this special structure can also provide more active sites and exhibit better electrocatalytic performance due to its high surface area-to-volume ratio and unique structural features. , For instance, Qiu et al employed a sacrificial template strategy to carbonize urea-doped phenolic resin (UPR), resulting in N-doped mesoporous hollow carbon spheres (Co/NMHCS) as a multifunctional electrocatalyst.…”