Chitosan as a biomass-based bridge: integrating CO₂ capture and electrochemical upgrading

INTRODUCTION

Electrochemical CO₂ reduction reaction (CO₂RR) can convert waste CO₂ into fuels and chemicals. However, its industrial viability is limited by poor CO₂ solubility, sluggish mass diffusion, and low selectivity toward multi-carbon (C₂₊) product^[1,2]. It is urgently needed to design innovative electrode, which can enhance local CO₂ concentration, stabilize intermediates, and facilitate mass/electron transfer^[2,3]. Chitosan is a natural polysaccharide rich in -NH₂ and -OH. Chitosan-derived amine-functionalized foams achieve efficient CO₂ capture via hydrogen bonding and acid–base interactions^[4]. In CO₂RR, chitosan serves as a C/N source, a structure-inducing agent, and an ion-conductive binder^[1-3,5]. Therefore, chitosan can act as a “biomass bridge” integrating upstream CO₂ capture with downstream electroreduction.

In this article, a brief summary of the key characteristics of chitosan-derived materials applied in CO₂ capture and CO₂RR is presented. Based on this, an integrated electrode is proposed: 3D macroporous chitosan foam is used as the CO₂ capture trap, chitosan-derived mesoporous material is used as the CO₂ enrichment area and mass transfer pathway, and active sites close to this layer are used as the main interface for CO₂RR, resulting in product upgrading. This design concept provides new insights into creating CO₂-rich microenvironments for enhanced kinetics and selectivity. We hope this perspective can inspire further research into biomass-derived multifunctional materials for carbon capture and utilization, accelerating the transition toward a circular carbon economy.

CHITOSAN-DERIVED MATERIALS FOR CO₂RR OR CO₂ CAPTURE

Chitosan-derived electrocatalysts play multiple unifying roles through constructing rich mass transfer pathways and regulating the microenvironment of active sites, achieving efficient or highly selective generation of various products [Supplementary Table 1]. Firstly, chitosan is an excellent source of carbon and nitrogen. Upon pyrolysis, chitosan forms 3D porous carbon that stabilizes metal nanoparticles via strong metal–support interactions^[1]. Its amino groups like pyridinic-N, can activate CO₂ to enhance CO₂RR performance^[2]. Secondly, chitosan is a structure-inducing agent. It chelates metal ions and directs the growth of vertically aligned 3D structure on gas diffusion layers, which increases electrochemical surface area (ECSA), facilitates CO₂ diffusion, and protects the hydrophobic layer^[3]. Finally, Chitosan is an ion-exchange binder. In the latest report, chitosan was coated on the surface of Cu NPs, reducing the oxidation rate of Cu, while its hydrophilic, ion-conductive nature can increase the local CO₂/CO concentration [Figure 1A]^[5].

Figure 1. (A) Cu-chitosan, Cu-cellulose and Cu-chitin electro-catalyze the transformation of CO₂ into C₂₊ products. Reproduced from Ref.^[5], Copyright 2026, Springer Nature; (B) N-functionalized chitosan biochars have high CO₂ adsorption capacity. Reproduced from Ref.^[6], Copyright 2025, ACS Publications. FE: Faradaic efficiency; HER: hydrogen evolution reaction; NPs: nanoparticles.

Chitosan-based adsorbents exhibit efficient, reversible CO₂ capture ability due to high surface area, nitrogen functionality, and amine-rich surfaces [Supplementary Table 2]. On the one hand, chitosan can prepare 3D hierarchically porous adsorbents combined with other materials via hydrothermal treatment and carbonization^[4]. It acts as a renewable C/N source, creating micro/mesopores during decomposition, and residual N-groups serve as basic adsorption sites, which make adsorbents possess excellent stability and selectivity. On the other hand, amine-functionalized chitosan-based composites can further enhance CO₂ capture ability. In general, chitosan serves as a structural scaffold, provides initial amine sites, and acts as a matrix for additional amines [polyethylenimine (PEI), dopamine], boosting uptake via carbamate formation [Figure 1B]^[6].

FUTURE PERSPECTIVES: TOWARD INTEGRATED CO₂ CAPTURE AND CONVERSION

The above content reveals striking commonalities: chitosan is a renewable C/N source, a structural scaffold for hierarchical porosity, and a functional matrix with abundant amine groups. Thus, an integrated platform for CO₂ capture and CO₂RR upgrading can be constructed by fully leveraging the chelating ability, porous network formation and electron-donating amines of chitosan.

We propose a conceptual bifunctional gas diffusion electrode (GDE) with three hierarchical components [Figure 2]: (i) a macroporous chitosan foam or carbonized network for capturing CO₂ via amine-mediated chemisorption; (ii) a meso-/microporous N-doped carbon matrix for further concentrating CO₂; (iii) embedded metallic sites to transform CO₂ to C₂₊ products. This design eliminates separate capture/compression steps, feeding concentrated CO₂ directly to catalytic sites. In the actual operating device, the saturation state of capture layer and the continuous consumption of CO₂ at metallic active sites, both under the guidance of the electric field, facilitate the directional transport of CO₂.

Figure 2. The integrated platform for CO₂ capture and CO₂RR upgrading. CO₂RR: CO₂ reduction reaction.

In mechanism, the intrinsic properties of chitosan create a localized CO₂-rich microenvironment at catalytic interface. First of all, tunable porosity balances adsorption capacity with rapid diffusion, and chelation allows precise anchoring of metal active sites. Moreover, the amine groups bind CO₂ reversibly and generate a local alkaline environment upon quaternization, and nitrogen functionalities stabilize intermediates via hydrogen bonding, lowering asymmetric C–C coupling barriers, which suppresses hydrogen evolution reaction (HER) and steers selectivity toward C₂₊ products^[2]. Comparing amine-functionalized electrodes, ionic-liquid/polymer-modified electrodes, or metal–organic framework (MOF)/covalent organic framework (COF)-derived capture–conversion materials, chitosan-derived electrodes have remarkable multifunctionality, low cost and environmental friendliness, and are expected to achieve cost reduction and efficiency improvement while integrating capture and conversion^[7-9].

The integrated platform bypasses CO₂ solubility/diffusion limitations, shortens diffusion paths, opening a new paradigm for sustainable CO₂ valorization. However, there are several challenges and opportunities remaining:

1. The trade-off between capture capacity and catalytic activity needs optimization. The high amine loading may block active sites or alter hydrophilicity. Systematic studies on amine density, porosity, and performance are needed.

2. A thorough study is required for the long-term stability under the simultaneous capture/reduction conditions. For instance, when CO₂ chemisorption and cathodic potential act simultaneously, amine groups may undergo degradation. In-situ characterization methods [Raman, Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS)] and solid-state ¹³C nuclear magnetic resonance (NMR) techniques should be used to verify whether chitosan exists stably in the catalytic electrode^[5,10].

3. The scalability to larger electrode areas and industrially relevant current densities (> 500 mA·cm^-2) must be demonstrated, along with techno-economic and life-cycle assessments.

4. The design concept of the integrated platform should be extended to the utilization of other biomass polymers (such as cellulose, alginate) and other technical routes of CO₂ conversion (such as photocatalysis, thermal catalysis).

CONCLUSION

Chitosan is a multifunctional carbon-nitrogen framework rich in amino groups. It leads us to propose an integrated bifunctional GDE that combines efficient capture with direct electrochemical upgrading, which can build a CO₂-rich microenvironment with stabilized intermediates, enhancing kinetics and selectivity. While challenges in optimization, stability, and scale-up remain, this integrated platform represents a promising pathway toward sustainable CO₂ valorization and a circular carbon economy.