Construction of Fe-doped CoP with hybrid nanostructures as a bifunctional catalyst for overall water splitting

Modulating space charge of FeP/CoP p-n heterojunction for boosting oxygen evolution reaction

Surface reconstruction of electrocatalysts is an effective strategy to modulate the space charge distribution to enhance the electrocatalytic activity. The p-n heterostructured FeP/CoP-2D octagonal nanoplates were successfully constructed by cation-exchange method. The space charge effect caused by the p-n heterojunction accelerated the electron transfer, optimized the electronic structure, and improved the activity of the active sites during the oxygen evolution reaction process. As a result, FeP/CoP-2D required only 247 mV overpotential to achieve a current density of 10 mA cm-2 with a Tafel slope as low as 68 mV dec-1. Density-functional theory calculations confirmed that the construction of p-n heterojunctions can enhance the adsorption of *OH in the active centers and optimize the Gibbs free energy of the OER reaction. This study provides an effective and feasible strategy for constructing p-n heterojunctions to modulate the space charge state for optimizing the OER performance of electrocatalysts.

Strongly Coupled Heterostructured CoP/MoO2 as an Advanced Electrocatalyst for Urea-Assisted Water Electrolysis

Developing low-cost electrocatalysts with excellent activity and durability in urea-assisted water splitting is urgently needed in order to achieve sustainable hydrogen production. Herein, we in situ synthesized a robust coupled heterostructured electrocatalyst (CoP/MoO2) on a nickel foam (NF) substrate and explored its electrocatalytic performances in the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and urea oxidation reaction (UOR). The overpotential of CoP/MoO2/NF is found to be only 11 mV at 10 mA cm-2 during the HER process, which is significantly lower than that of commercial Pt/C. Meanwhile, the UOR catalytic performance of CoP/MoO2/NF indicates fast reaction kinetics, along with a considerable low driving potential (1.26 V) compared to that of the OER (1.51 V). In situ and ex situ techniques demonstrate that these excellent electrocatalytic properties are mainly ascribed to the effective synergistic coupled effect and strong electronic interactions between single-component CoP and MoO2, which can tune electronic states of Co and Mo, expose more active sites, enhance intrinsic catalytic activity, and accelerate charge transfer. Moreover, when used in electrochemical overall water splitting and urea-assisted water electrolysis, CoP/MoO2/NF can reach a current density of 10 mA cm-2 at only 1.46 and 1.32 V. This outperforms Pt/C||RuO2 and numerous nonprecious metal electrocatalysts and maintains a stable long-term electrolytic operation for 84 h. This work provides a promising pathway for the development of efficient catalysts during urea-assisted water electrolysis for hydrogen production.

Bio-inspired design of NiFeP nanoparticles embedded in (N,P) co-doped carbon for boosting overall water splitting

The design and synthesis of cost-effective and stable bifunctional electrocatalysts for water splitting via a green and sustainable fabrication way remain a challenging problem. Herein, a bio-inspired method was used to synthesize NiFeP nanoparticles embedded in (N,P) co-doped carbon with the added carbon nanotubes. The obtained Ni_0.8Fe_0.2P-C catalyst displayed excellent hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performances in both alkaline and alkaline simulated seawater solutions. The optimal Ni_0.8Fe_0.2P-C/NF only needs overpotentials of 45 and 242 mV to reach the current density of 10 mA cm^-2 under HER and OER working conditions in 1.0 M KOH solution, respectively. First-principles calculations revealed the presence of a strong interaction between the carbon layer and metal phosphide nanoparticles. Benefiting from this and carbon nanotubes modification, the fabricated Ni_0.8Fe_0.2P-C presents impressive stability, working continuously for 100 h without collapse. A low alkaline cell voltage of 1.56 V for the assembled Ni_0.8Fe_0.2P-C/NF//Ni_0.8Fe_0.2P-C/NF electrocatalyzer could afford a current density of 10 mA cm^-2. Moreover, when integrated with a photovoltaic device, the bifunctional Ni_0.8Fe_0.2P-C electrocatalyst demonstrates application potential for sustainable solar-driven water electrolysis.

Iron-Cobalt-Cerium Multimetallic Oxides Derived from Prussian Blue Precursors: Enhanced Oxygen Evolution Electrocatalysis

Exploring non-precious metal-based electrocatalysts is still challenging in 21^st century. In this work, a series of hexagonal bipyramidal Ce-based PBA materials as precursors with different Fe/Co metal ratios, namely as CeFe_x Co_1-x -PBA, are successfully constructed via co-precipitation method and converted into corresponding metal oxides (denoted as Fe_x Co_1-x CeO_y ) via thermal treatment. Then, they as electrocatalysts realize highly efficient oxygen evolution reaction (OER). Especially, as-synthesized Fe_0.7 Co_0.3 CeO_y electrocatalyst shows very low overpotentials of 320 mV at the current density of 10 mA cm^-2 and the Tafel slop of 98.4 mV dec^-1 in 1 M KOH with remarkable durability for 24 h, which was due to the synergistic effect of multi-metal FeCoCe centers. Furthermore, a two-electrode cell of Fe_0.7 Co_0.3 CeO_y /NF||Pt/C/NF realizes outstanding overall water splitting with a voltage of only 1.71 V at 10 mA cm^-2 and remarkable long-term durability, that is even superior to benchmark IrO₂ /NF||Pt/C/NF counterpart.