Tannic Acid-Mediated In Situ Controlled Assembly of NiFe Alloy Nanoparticles on Pristine Graphene as a Superior Oxygen Evolution Catalyst

Abstract

Controlled assembly of small and highly dispersed earth-abundant transition metal-based oxygen evolution reaction (OER) catalysts on pristine graphene could greatly boost the OER efficiency while significantly reducing the cost, but this presents great challenges. Pristine graphene (rather than reduced graphene oxide or graphene with a damaged electronic structure) supported NiFe alloy nanoparticles (NPs) have been synthesized for the first time via tannic acid (TA)-mediated in situ controlled assembly, in which TA not only noncovalently modifies the graphene to strongly coordinate with Ni 2+ and Fe 2+ but also in situ reduces these metal ions to alloy NPs. The chemical composition of these alloy NPs can be tailored via changing the ratio of Ni 2+ and Fe 2+ in the reaction. These nanohybrids show ultrahigh and tunable OER catalytic activities. The optimum one obtained using the ratio of 9:1 achieves 10 mA cm −2 at an overpotential of 246 mV and shows a Tafel slope of 46 mV dec −1 , both of which are lower than those of most reported OER catalysts, including state-of-the-art Ru-and Ir-based ones. In addition, this catalyst exhibits little change of the overpotential after 20 h of chronopotentiometric measurement (from 246 to 258 mV at 10 mA cm −2 ) and negligible current loss after 1000 CV cycles (from 123.3 to 133.4 mA cm −2 at 1.54 V). The superior catalytic activity and durability are ascribed to the in situ assembled small, highly dispersed, and highly conductive NiFe alloy NPs on pristine graphene significantly facilitating the electron transfer and increasing the electrochemically accessible active sites, the doped FeOOH remarkably promoting the intrinsic activity of Ni(OH) 2 on the surface of these alloy NPs, and the robust in situ growth greatly enhancing the durability during the OER testing. This work provides a green, facile, and economical strategy to controllably fabricate low-cost and high-performance OER catalysts and also sheds light on the performance enhancement mechanism from tunable OER catalytic activity.

The Scalable Solid-State Synthesis of a Ni5P4/Ni2P–FeNi Alloy Encapsulated into a Hierarchical Porous Carbon Framework for Efficient Oxygen Evolution Reactions

“…As shown in Figure 6 e, Ni 5 P 4 /Ni 2 P–FeNi@C presents a larger C dl value (8.01 mF cm −2 ) than Ni 5 P 4 /Ni 2 P–Fe–FeNi 3 @AC (4.54 mF cm −2 ), demonstrating an enhanced ECSA with more active sites, which may benefit from the hierarchical porous architecture caused by NaHCO 3 . Impressively, the OER catalytic activity of Ni 5 P 4 /Ni 2 P–FeNi@C in this work is comparable to and may even outperform recently reported alloy- and phosphide-composited catalysts ( Figure 6 f and Table 1 ) [ 14 , 19 , 22 , 29 , 30 , 32 , 33 , 34 , 35 ].…”

“…To further evaluate the catalytic properties, the OER dynamics were evaluated by Tafel slope. Ni 5 P 4 /Ni 2 P–FeNi@C exhibited the lowest Tafel slope of 46 mV dec −1 , as shown in Figure 6 c, indicating that Ni 5 P 4 /Ni 2 P–FeNi@C has the most rapid kinetics for the OER process [ 30 ]. These results may be caused by the in situ formation of NaCl and NaHCO 3 .…”

Recent Progress on NiFe‐Based Electrocatalysts for the Oxygen Evolution Reaction

“…4) Less mass transport between the alloy and the electrode. [144][145][146][147] Therefore, efficient approaches need to be developed to optimize the OER activities of NiFe alloys. Wang and co-workers found that hcpphase NiFe NPs encapsulated in N-doped carbon (NC) exhibited an unexpectedly low overpotential of 226 mV at 10 mA cm −2 in 1.0 m KOH as the electrolyte, in addition to an excellent stability during 35 h of continuous operation at a current density of 20 mA cm −2 .…”

Synthesis of Structurally Stable and Highly Active PtCo3 Ordered Nanoparticles through an Easily Operated Strategy for Enhanced Oxygen Reduction Reaction

“…8,19−24 In light of adverse Fenton reaction from Fe ions, 25 poisoning effect from leached Cu ions, 26 and inherent disordered structure of PtNi 3 , 27 PtCo 3 NP emerges as a promising cathode for fuel cells because of the low cost and mildness of Co 2+ to the proton-exchange membrane. Very little effort has been devoted to PtCo 3 , and previously reported dealloyed PtCo 3 NPs are in disordered face-centered cubic (fcc) structure; 28,29 traditional synthetic strategies, for example, impregnation method, 10,19 KCl matrices, 30 oxide coating, 31 freeze-drying− annealing, 28 and self-assembly, 32,33 show practicability for nanocatalyst preparation, meanwhile they suffer from complexity, time-consuming process, large particle sizes, or incomplete removal of oxide and Cl − . Hence, new strategies should be exploited to synthesize small-sized well-dispersed ordered Ptbased NPs in a practical and easily operated way.…”

“…Very little effort has been devoted to PtCo 3 , and previously reported dealloyed PtCo 3 NPs are in disordered face-centered cubic (fcc) structure; , thus, it remains essential to construct ordered intermetallic PtCo 3 NPs. Furthermore, although traditional synthetic strategies, for example, impregnation method, , KCl matrices, oxide coating, freeze-drying–annealing, and self-assembly, , show practicability for nanocatalyst preparation, meanwhile they suffer from complexity, time-consuming process, large particle sizes, or incomplete removal of oxide and Cl – . Hence, new strategies should be exploited to synthesize small-sized well-dispersed ordered Pt-based NPs in a practical and easily operated way.…”