How operando spectroscopy advances electrocatalysis for green hydrogen and carbon capture

In this article you’ll learn:

• Why the catalyst you synthesise may not be the catalyst driving the reaction.
• Why conventional characterisation alone cannot fully explain electrocatalytic performance.
• How operando spectroscopy is revealing active sites, transient intermediates and catalyst evolution under real-world operating conditions.
• Why mechanistic insight is essential for developing the next generation of electrocatalysts.

A catalyst characterised before an electrochemical process may not be the catalyst responsible for the reaction. The applied potential, electrolyte composition and adsorbed intermediates can affect surface morphology, oxidation state and coordination environment, yet conventional characterisation only captures the active material before or after operation. Catalytic performance can be observed without knowing which active sites, interfaces or reaction pathways were responsible, making development of improved or innovative catalysts more challenging.

Operando spectroelectrochemistry helps close this gap by observing chemical and structural changes at the same time electrochemical performance is measured. It increasingly supports developments in green electrochemistry, where the availability of renewable electricity is driving new advancements in low‑carbon chemical production.

This article looks at three areas where operando techniques are changing how electrocatalysts are developed:

• Green hydrogen through water splitting (water electrolysis).
• Conversion of captured CO₂ into useful chemicals.
• Recovery or conversion of waste streams into valuable commodities.

Why promising electrocatalysts remain difficult to scale from the laboratory to industry

Global installed electrolysis capacity doubled in 2025, yet low-emissions hydrogen production remains at only 1% of the worldwide total,¹ partly reflecting the considerable technical challenges in the field.

Commercially relevant electrocatalysis requires optimisation of multiple relevant parameters and must be translatable to large-scale production. A viable process has to balance three key areas:

• Reaction rate, selectivity and Faradaic efficiency (the fraction of transferred charge that produces the intended product).
• Energy efficiency, usually measured through overpotential, because excess potential to reach the target reaction rate means wasted energy and cost.
• Material availability and operational lifetime.

For industrial deployment, these features must all hold up at realistic current densities and throughputs. During development, researchers therefore need to understand how the electrode–electrolyte interphase evolves; which intermediates belong to the productive pathway (and which do not); and whether results can be repeated across electrodes, cells and operating cycles. Equally important is identifying the true active site and the rate-limiting step that governs catalytic performance. Answering these questions presents a range of technical challenges, especially as it requires making measurements in a dynamic system.

Water splitting: resolving the HER and OER bottlenecks

Water splitting, or electrolysis, stores electrical energy in chemical form through two half-reactions occurring at the opposing electrodes:

• Oxygen evolution reaction (OER) at the anode: 2H₂O → O₂ + 4H⁺ + 4e⁻
• Hydrogen evolution reaction (HER) at the cathode: 2H⁺ + 2e⁻ → H₂
• Overall reaction: 2H₂O → 2H₂ + O₂

While both half-reactions must be efficient for economical green hydrogen production, the OER remains a key bottleneck, and its sluggish kinetics and high energy demand (due to large overpotentials) require improvement to lower costs and promote wider adoption.²

Moreover, optimising the OER and HER involves distinct technical and analytical challenges. The OER requires four electron transfers as well as dynamic metal–oxygen bonding, whereas the HER critically depends on hydrogen adsorption, proton or water activation, and local organisation at the electrolyte interface.

Scientists therefore need to monitor potential-induced catalyst reconstruction, changes in metal oxidation state and coordination, interfacial water dynamics and catalyst degradation, further understanding these processes during prolonged operation under industrially relevant conditions.

Recent advances in operando studies of HER and OER

Zhao and co-workers used combined bulk and surface-sensitive operando methods, including Raman spectroscopy, to show that for cobalt OER catalysts, tetrahedral Co^II centres undergo dynamic transformation under potential into highly active Co^IV intermediates that represent the catalytically active species.³ Partial iron incorporation increased catalytic activity by stabilising the Co^IV centres. Another study used SEC-FTIR to detect formation of hydroxide species on the surface of cobalt sulfide catalysts during the OER, with accompanying morphological changes that were tracked by transmission electron microscopy (TEM).⁴ Likewise, operando work on CoAl layered double hydroxides revealed substantial structural and oxidation state evolution during the electrocatalytic alkaline OER.⁵

Other researchers studied nitrogen-doped molybdenum clusters supported on Ti₂C₂T_x as HER electrocatalysts. Operando X-ray absorption spectroscopy and in situ Raman measurements showed that the catalyst evolved under working conditions to expose more active sites, achieving comparable performance to commercial Pt/C.⁶

An important learning is that the synthesised catalytic material may be a precursor to the true working catalyst. This insight could not have been obtained without operando analysis, which emphasises its wider significance because the same questions on active phase formation and dynamics arise in fuel-cell electrodes and other electrochemical devices.

How operando spectroscopy is improving CO₂ reduction: steering carbon towards useful products

The carbon dioxide reduction reaction (CO₂RR) is a key utilisation pathway within carbon capture, utilisation, and storage (CCUS). It converts captured or concentrated CO₂ into high-value chemical feedstocks such as carbon monoxide, formate, alcohols and hydrocarbons. If integrated with suitable capture and renewable power systems, it could contribute significantly to the circular carbon economy. However, chemical selectivity remains the central challenge to electrocatalytic solutions.

The CO₂RR involves branching proton and electron transfer pathways that are in direct competition with the HER, which draws on the same electron and proton donors at the cathode. Therefore, multiple operating parameters can profoundly influence the product distribution, including local pH, electrolyte composition and interfacial water structures.

Controlling reactivity becomes even more difficult for multi-carbon (C₂+) products. Although copper is notable among electrocatalytic metals in promoting C₂+ product formation, adsorbed C₁ intermediates must still meet in favourable configurations for carbon–carbon bonds to form. Thus, adsorbed CO coverage, orientation and residence time all play a role, and when developing new catalysts or electrocatalytic processes, it is crucial to distinguish whether detected species are productive intermediates, ‘spectators’ or surface poisons.

Recent advances in operando CO₂ reduction research

Modifying the electrolyte can significantly alter reaction pathways. Mohandas and colleagues reported that adding 15% N,N-dimethylformamide (DMF) to the electrolyte raised CO₂RR Faradaic efficiency from 67% to 94%.⁷ Using in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), which probes surface intermediates and interfacial water organisation, they deduced that DMF disrupts the hydrogen bonding network at the cathode interface, thereby disfavouring the HER.

Other researchers attained 74% Faradaic efficiency of C₂+ products by adding iodide, applying ATR-SEIRAS to show that adsorbed I⁻ increases CO adsorption strength to promote C–C coupling.⁸

Catalyst morphology is equally important. Zhang and co-workers employed operando powder X‑ray diffraction and micro-Raman spectroscopy to study Cu₂O nanocatalysts, finding that octahedral and cubic geometries favoured ethylene production or the HER pathway, respectively.⁹ A related study achieved 36% enhancement in Faradaic efficiency for C₂+ products by using high-curvature Cu nanoparticles.¹⁰ Operando Raman spectroscopy, supported by density functional theory (DFT) calculations, indicated these surfaces promote stabilisation of *CO intermediates and lower the energy barriers for C–C coupling.

These examples illustrate how even small changes in the physical catalyst material and its interactions with the electrolyte can profoundly affect reactivity and chemical selectivity.

How operando methods support electrocatalytic waste valorisation

Battery black mass and related leachates contain valuable lithium, cobalt, nickel and other materials. Efficient recovery is complicated by batch variability, as well as binders and other components, and current recycling technologies remain limited in commercial scope due to low efficiency and scalability.¹¹

Nevertheless, reclaimed materials derived from Li-ion batteries could generate useful new electrocatalysts if the challenges can be overcome. Multiple recent research efforts have explored such materials for the OER and HER,¹² in some cases achieving comparable performance to commercial electrocatalysts.

In one example, Wang and co-workers transformed cobalt oxalates from black mass into cobalt nitride nanoparticles that outperformed commercial RuO₂ in the alkaline OER.¹³ Other researchers used lithium electrochemical tuning to convert spent mesoporous carbon anodes from Li-ion batteries into highly active nitrogen reduction electrocatalysts, offering a promising route to green ammonia.¹⁴

As familiar analytical challenges affect electrocatalyst development for upcycling, in situ and operando methods are gaining attention as the field accelerates. Recently, Kang and colleagues explored electrochemical conversion of polyethylene terephthalate (PET)-derived intermediates into two prominent amide feedstocks, formamide and glycolamide, by introducing ammonia into the process.¹⁵ In situ Raman spectroscopy, supported by DFT calculations, identified the rate-determining step as dehydrogenation of adsorbed *NH₃ to *NH₂, which could inform future development of catalysts with enhanced performance.

In sum, recycling or upcycling of waste streams shows promise as a source of both new electrocatalytic technologies and low-carbon chemical feedstocks.

Why operando spectroscopy works best alongside complementary analytical techniques

No operando technique answers every mechanistic question, but vibrational spectroscopy, including infrared (IR) and Raman modes, is especially valuable for examining adsorbed electrolyte species and chemical changes at electrode surfaces (Table 1). Cell construction, optical configuration and measurement conditions must be carefully controlled, however, as they can strongly affect results.¹⁶ Other common operando methods that can provide complementary information include:

• Electrochemical impedance spectroscopy, which probes kinetic and transport behaviour.
• X-ray absorption spectroscopy (XAS) or X-ray photoemission spectroscopy (XPS), which track oxidation states and coordination environments.
• X-ray diffraction (XRD), which follows crystalline phases and may be combined with microscopy to reveal structural and morphological changes.
• Chromatography or mass spectrometry, to identify and quantify released chemical species.

The strongest conclusions come from combining complementary techniques. Observed spectral changes should correlate with viable reaction pathways or product formation and, where possible, be independently verified using complementary analytical methods.

Conclusion: from catalyst screening to mechanism-led development

Electrochemical technologies will not achieve commercial scale through activity measurements alone. Operando methods are vital to revealing how active sites, intermediates and interfaces evolve under load, allowing researchers to move from screening nominal materials towards designing and realising high-performance, operationally robust electrocatalysts that can meet the growing demand for sustainable chemical production.

Key takeaways:

• Different electrochemistries encounter common measurement challenges, regardless of the reaction being studied.
• Catalysts can restructure under operating conditions, meaning the active site responsible for performance may only exist while the electrochemical cell is under potential.
• Understanding catalyst behaviour requires more than electrochemical performance data alone. Researchers must also observe how intermediates, interfaces and active phases evolve during operation. Operando vibrational spectroscopies, including SEC-FTIR, SEC-Raman and ATR-SEIRAS, provide molecular-level insight that is particularly powerful when combined with complementary analytical techniques.
• Better mechanistic understanding supports the development of more selective, durable and efficient electrocatalysts for low-carbon chemical production.

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