A Universal Strategy for Carbon-Supported Transition Metal Phosphides as High-Performance Bifunctional Electrocatalysts towards Efficient Overall Water Splitting

Abstract

Exploring cost-effective and general approaches for highly active and stable bifunctional transition metal phosphide (TMP) electrocatalysts towards overall water splitting is greatly desirable and challenging. Herein, a general strategy combining sol–gel and a carbonization-assisted route was proposed to facilely fabricate a series of TMP nanoparticles, including CoP, MoP, FeP, Cu2P, Ni2P, PtP2, FeNiP, CoNiP, and FeCoNiP, coupled in an amorphous carbon matrix with one-step carbon composite formation. The resultant NiFeP@C exhibits excellent activities as a bifunctional electrocatalyst toward oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) with low overpotentials of 260 and 160 mV, respectively, at 10 mA/cm2 in 1 M KOH solution. With the NiFeP@C electrocatalyst as both electrode materials, an integrated electrolyzer can deliver 47.0 mA/cm2 of current density at 1.60 V, better than the assembled Pt/C20∥IrO2 counterpart. The encapsulation of NiFeP nanoparticles in the carbon matrix effectively prevents their corrosion and leads to almost unfading catalytic activities for more than 20 h for either the HER, OER, or overall water splitting, outperforming recently reported bifunctional electrocatalysts. The coexistence of Ni, Fe, P, and C would have synergetic effects to accelerate charge transfer and promote electrocatalytic activity. This universal strategy for TMP-based composites opens up a new avenue to explore TMPs as multifunctional materials for various applications.

Promotion effect of metal phosphides towards electrocatalytic and photocatalytic water splitting

“…Kang et al 41 proposed a universal but facile and controllable sol‐gel strategy (Figure 5) to fabricate carbon‐supported metal phosphides with different metal ions as metal sources. During the sol‐gel process, citric acid chelated with metal ions to form cross‐linked networks in which the inorganic species were homogeneously dispersed.…”

“…Preparation diagram of metal phosphide@C. Reproduced with permission: Copyright 2020, American Chemical Society 41 …”

High Density and Unit Activity Integrated in Amorphous Catalysts for Electrochemical Water Splitting

“…To find a solution to these challenges, some durable bifunctional electrocatalysts of metal oxides/hydroxides, sulfides, selenides, phosphides, and borides [ 161–166 ] based on 3D transition metals that could simultaneously catalyze both the OER and HER in the same electrolyte have been implemented. Nevertheless, the catalytic activities of these catalysts are still less than those of noble‐metal‐based catalysts.…”

Increasing Electrocatalytic Oxygen Evolution Efficiency through Cobalt‐Induced Intrastructural Enhancement and Electronic Structure Modulation

“…The raw materials needed for EWS are not only abundantly available, but energy conversion from electrical to chemical energy can also effectively fill the large gaps in energy supply requirements [7–10] . However, as an indispensable half‐reaction in EWS systems, the oxygen evolution reaction (OER) at the anode involves a multi‐electron transfer process with a high electrochemical energy barrier; it thus requires an advanced electrocatalyst to accelerate the sluggish kinetics of the overall reaction [11–14] . Although noble‐metal Ir/Ru‐based materials are considered as benchmark OER catalysts, they are extremely scarce, and exorbitant market prices severely impede their commercial application.…”

“…[7][8][9][10] However, as an indispensable half-reaction in EWS systems, the oxygen evolution reaction (OER) at the anode involves a multielectron transfer process with a high electrochemical energy barrier; it thus requires an advanced electrocatalyst to accelerate the sluggish kinetics of the overall reaction. [11][12][13][14] Although noble-metal Ir/Ru-based materials are considered as benchmark OER catalysts, they are extremely scarce, and exorbitant market prices severely impede their commercial application. Therefore, substantial efforts have been made to explore highly active and inexpensive catalysts that can replace traditional noble metals.…”