Bifunctional Electrocatalysts for Overall and Hybrid Water Splitting

Abstract

Electrocatalytic water splitting driven by renewable electricity has been recognized as a promising approach for green hydrogen production. Different from conventional strategies in developing electrocatalysts for the two half-reactions of water splitting (e.g., the hydrogen and oxygen evolution reactions, HER and OER) separately, there has been a growing interest in designing and developing bifunctional electrocatalysts, which are able to catalyze both the HER and OER. In addition, considering the high overpotentials required for OER while limited value of the produced oxygen, there is another rapidly growing interest in exploring alternative oxidation reactions to replace OER for hybrid water splitting toward energy-efficient hydrogen generation. This Review begins with an introduction on the fundamental aspects of water splitting, followed by a thorough discussion on various physicochemical characterization techniques that are frequently employed in probing the active sites, with an emphasis on the reconstruction of bifunctional electrocatalysts during redox electrolysis. The design, synthesis, and performance of diverse bifunctional electrocatalysts based on noble metals, nonprecious metals, and metal-free nanocarbons, for overall water splitting in acidic and alkaline electrolytes, are thoroughly summarized and compared. Next, their application toward hybrid water splitting is also presented, wherein the alternative anodic reactions include sacrificing agents oxidation, pollutants oxidative degradation, and organics oxidative upgrading. Finally, a concise statement on the current challenges and future opportunities of bifunctional electrocatalysts for both overall and hybrid water splitting is presented in the hope of guiding future endeavors in the quest for energy-efficient and sustainable green hydrogen production.

Unlocking enhanced electrochemical performance through oxygen–nitrogen dual functionalization of iron–nickel–sulfide for efficient energy storage systems

“…The irregularities on the surface cause diffuse scattering, which is recorded as noise. 37 Moreover, the FNMS and FNMOS XRD profiles did not reveal any other phases, suggesting that any metal sulfide phases present are in the form of an amorphous shell, with an FNM core. Meanwhile, by analyzing the diffraction peak in the range of 34–38 2 θ degrees or the (410) plane (Fig.…”

In Operando X-ray Spectroscopic and DFT Studies Revealing Improved H2 Evolution by the Synergistic Ni–Co Electron Effect in the Alkaline Condition

“…H 2 evolution from water electrolysis is a traditional but direct way to produce clean energy for meeting global energy crisis. 1 − 3 By referring to the prediction in Yan’s work, Ni- and Co-based pyrites (NiS 2 and CoS 2 ) can be good candidates for efficient HER in acidic media. 4 − 10 Unfortunately, the oxygen evolution reaction (OER) over the Ni- and Co-based pyrite electrocatalysts is usually conducted in the alkaline electrolytes for high efficiency.…”

“…Hydrogen gas (H 2 ) is the cleanest source for energy generation without carbon emission, hence urging the technique development of the hydrogen evolution reaction (HER). H 2 evolution from water electrolysis is a traditional but direct way to produce clean energy for meeting global energy crisis. − By referring to the prediction in Yan’s work, Ni- and Co-based pyrites (NiS 2 and CoS 2 ) can be good candidates for efficient HER in acidic media. − Unfortunately, the oxygen evolution reaction (OER) over the Ni- and Co-based pyrite electrocatalysts is usually conducted in the alkaline electrolytes for high efficiency. − Such two conflicting conditions unlikely lead to efficient total water splitting. In this regard, seeking durable and active HER electrocatalysts to align the alkaline conditions of the OER can be one of the solutions.…”

Self-supported Ru-doped NiMoO4 for efficient hydrogen evolution with 1000 mA cm−2 at a low overpotential

“…10–12 Therefore, highly efficient HER and OER electrocatalysts are required to reduce the overall energy consumption for hydrogen production. 13–15…”