Chemical Fermentation Pore Creation on Multilevel Bio-Carbon Structure with In Situ Ni-Fe Alloy Loading for Superior Oxygen Evolution Reaction Electrocatalysis

Abstract

In the quest for high-efficiency and cost-effective catalysts for the oxygen evolution reaction (OER), a novel biomass-driven strategy is developed to fabricate a unique one-dimensional rod-arrays@two-dimensional interlaced-sheets (C1D@2D) network. A groundbreaking chemical fermentation (CF) pore-generation mechanism, proposed for the first time for creating nanopores within carbon structures, is based on the optimal balance between gasification and solidification. This mechanism not only results in a distinctive C1D@2D multilevel network with nanoscale, intersecting and freely flowing channels but also introduces a novel concept for in situ, extensive and hierarchical pore formation. The unique architecture, combined with the homogeneous dispersion of Ni-Fe nanoparticles, facilitates easy electrolyte penetration and provides abundant active sites for the anchoring and dispersion of reactive molecules or ions. Consequently, the Ni-Fe@C1D@2D porous network demonstrates an exceptional OER electrocatalytic performance, achieving a record-low overpotential of 165 mV at 10 mA cm−2 and maintaining long-term stability for over 90 h. Theoretical calculations reveal that the porous structure markedly strengthens the interaction between alloy nanoparticles and the carbon matrix, thereby significantly boosting their electrocatalytic activity and stability. These findings unequivocally validate the CF pore-generation mechanism as a powerful and innovative strategy for designing highly efficient functional nanostructures.

1. Introduction

Environmental pollution and climate issues stemming from oil consumption, along with energy crisis, have stimulated intensive researches on the renewable energy technologies [1–3]. Hydrogen energy, as a clean, efficient and reproducible energy, has become an attractive measure for solving the energy supply security and the greenhouse gas reduction [4–6]. Water electrolysis, a promising hydrogen-producing technology on large scale, involves hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), in which the latter is the kinetically rate-limiting step owing to its four-electron-transfer process [7, 8]. Thus, exploring highly efficient OER electrocatalysts then becomes a significant demand [9–11].

Overpotential (η) is one of the most critical parameters to evaluate electrocatalysts’ OER activity, and a lot of efforts have been made to synthesize electrocatalysts with low overpotential. Loading active substance on conductive substrate is considered to be beneficial to reduce the overpotential due to high catalyst loading and low electric conductivity. For examples, overpotentials of 154 mV at 10 mA cm−2 have been achieved by Ni foam electrodes with loading of amorphous (Ni, Fe)OOH or FeP/Ni2P [12, 13]. However, loading the active materials onto the foam substrate is usually difficult or fussy, not universal for most of the electrocatalysts, which limits its application scope. More non-supported catalysts have attracted lots of efforts [14–16]. However, the decrease of overpotential is quite difficult and the reported overpotential is usually higher than 200 mV at 10 mA cm−2. Very recently, Qin’s group reported a novel fabrication of mesoporous single crystal with lots of active edges around the mesopores by Fe modification and achieved an ultralow η of 185 mV at 10 mA cm−2 [17]. No electrocatalysts on non-supported inert electrode with overpotential less than 180 mV at 10 mA cm−2 have been reported. Constructing special structures to further decrease overpotential is still a research focus, but proved to be a big challenge so far.

Recently, bimetallic alloy catalysts, such as NiFe, NiCo and FeCo, exhibit superior activity in comparison to their individual constituents, probably because the co-existence of two different metals can adjust th