The persistent escalation of the worldwide energy crisis necessitates the advancement and implementation of sustainable renewable energy conversion technologies. Researchers and engineers are currently exploring novel energy resources, with solar and wind energy emerging as the most auspicious sources of renewable energy ^[1][2][1,2]. However, solar energy is constrained by many factors which limit its commercial applications, such as diurnal and seasonal variations, special requirements of geographical location, and other environmental problems. Furthermore, it suffers from relatively low energy flow density, suboptimal efficiency, and high costs ^[3][4][3,4]. Wind energy is facing obstacles such as the variability of wind speed, noise problems, and intermittent power generation. Moreover, effective utilization of wind energy necessitates the integration of energy storage systems to ensure efficient and reliable operation [5]. Compared with wind and solar energy, electrochemical techniques have emerged as promising solutions for energy storage and conversion owing to their several advantages ^[6][7][8][9][6,7,8,9]. For instance, supercapacitors offer high power density, rapid charge and discharge rates, extended longevity, and secure operation ^[10][11][12][10,11,12]. Similarly, fuel cells provide superior energy capacity and higher energy density, coupled with a longer lifespan ^[13][14][13,14]. Electrochemical techniques present a viable means of both storing energy and converting renewable sources of energy, such as solar and wind, into electrical power for storage purposes ^[15][16][17][15,16,17]. Despite its advantages, the electrochemical method is beset by certain drawbacks that hinder its widespread adoption, e.g., low reaction activity, limited lifespan, high costs, and low energy density, which have yet to be adequately addressed ^[18][19][20][18,19,20].

In recent decades, researchers have focused on the catalyst and material aspects of electrochemical techniques, while the low mass transfer and charge transfer rates, which hinder the overall energy efficiency, are rarely discussed ^[8][21][8,21]. In conventional 2D electrodes within the electrochemical prototype, the planar current collector has good transfer properties in the 2D plane, and has a limited mass/charge transfer in the depth direction. When using a thicker electrode with a higher mass loading, only a part of the active material is utilized for energy storage due to inadequate charge delivery. Therefore, a 3D electrode structure, such as a 3D conductive scaffold or a 3D porous network, for ion transport can provide efficient charge delivery throughout the bulk volume of a thick electrode. This feature is advantageous for utilizing all electrode materials, regardless of their thickness, and for achieving high-rate and high-capacity energy storage [22].

Here, the ice-templated method (ITM) has drawn significant attention to the improvement of the electrochemical properties of various materials [23], and significant evidence for this can be seen in the increasing number of publications over time. The ITM approach is relatively straightforward and can produce hierarchically porous structures that exhibit superior performance in mass transfer, and the unique morphology has been shown to significantly enhance electrochemical performance, making it a promising method for energy storage and conversion applications [24]. ITM provides several notable advantages over conventional techniques for creating porous structures: (i) it is a green and sustainable process, which employs water ice crystals as a vacancy; (ii) it is a straightforward and easily scalable approach that affords a high degree of control over pore structure; and (iii) it is a cost-effective method that can be adapted to the manufacture of large volumes of materials, rendering it a viable and practical option for industrial applications ^[25][26][27][25,26,27].

ITM is a technique that utilizes a solvent to induce the formation of a second phase, such as polymers, ceramics, or metals, and promote crystal growth during solidification. The solvent crystals are then eliminated through sublimation, leaving behind a porous structure that mirrors the morphology of the solvent crystals. The microstructure of ice-templated materials is impacted by various factors, including the freezing source and conditions, which significantly influence the structure of the resulting aerogels [28]. The first step is to prepare a suspension of particles in a liquid, which is typically water or a solvent. The second phase is dispersed or dissolved in the solvent. Then the suspension is frozen at a controlled cooling rate, which affects the distribution of the ice crystals that will form during the freezing process. Finally, the frozen material is sublimated to remove the ice from the sample, resulting in a porous, structured material with the particle network preserved.

The type of second phase (suspended materials) can be varied for multi-applications. It can be, e.g., ceramic [29], which has low thermal conductivity, good corrosion resistance and considerable mechanical strength. Li et al. [30] reported TiN porous ceramics prepared via a freeze-drying and in situ nitridation reaction method using Ti powder and chitosan as raw materials. It showed great potential for use as sulfur host material for lithium–sulfur batteries, with a high capacity of 778 mAh/g. Judez et al. [31] reported a Li-ion conducting glass ceramic (LICGC)-based composite polymer electrolyte (CPE) that delivered high sulfur utilization and areal capacity.

Carbon nano-fibers are considered excellent nano-architectural substrates for supercapacitor applications due to their high power density, good electrochemical cyclic stability, and other desirable properties ^[28][32][33][28,32,33]. Qie et al. [34] synthesized porous carbon with high-level nitrogen doping using the ITM method as anode material for lithium-ion batteries, producing a reversible capacity of 943 mAh/g at a current density of 2 A/g even after 600 cycles. Wu et al. [35] constructed necklace-box structural FeS₂/WS₂-CNFs, which has resulted in high-performance anodes for LIBs, SIBs, and potassium-ion batteries; moreover, the special spatial confinement structure effectively alleviates volume expansion and protects the carbon shell from being destroyed.

Graphene/GO/reduced graphene oxide (rGO) [36] is regarded as a super lightweight and high conductivity material; it can be used in many applications, such as porous electrodes [30], supercapacitors [37], and sensors ^[38][39][40][38,39,40], etc. Chen et al. [41] presented an ice template method for fabricating flexible macroporous 3D graphene sponges as the anode of microbial fuel cells (MFC), where the graphene sponge was found to be conductive, lightweight, and could recover from deformation repeatedly up to 50%. These sponges generated higher power densities than carbon felt due to their unique porosity, which allows microbes to diffuse more easily inside them, leading better performance. Wang et al. [21] developed a graphene-supported electrode by the ice templating method, and the porous structure enhanced the Faradic efficiency by the promotion of mass transfer.

The metallic particles can be catalytic active sites and capacitors, and ITM treatment provides higher porosity with much lower agglomeration tendencies ^[34][42][34,42]. Li et al. [42] reported that a low-tortuous thick electrode can be successfully designed using a freezing drying route. These types of electrodes have straight lithium-ion transport channels, which allows for independence in electrode thickness and tortuosity. This design accelerates lithium-ion transport and reduces concentration polarization, resulting in excellent rate capability.

Polymer-based porous materials can provide functional groups as reaction active sites, which enhance the electrocatalytic activity and selectivity and offer crucial mechanical stability, flexibility, and durability for electrochemical cells. Colard et al. [43] demonstrated nanoparticle-reinforced soft polymer foams as chemical-sensor components, in which ITM guides and confines the assembly of colloids, resulting in the creation of armored composite self-supporting cellular structures with soft polymer composite matrixes.

ITM is a simple and effective fabrication process performed by adjusting the physical interactions between the suspension and the ice, and also by altering the cooling method of the material in order to control the pore morphologies [44]. The ice crystal growth influences the morphology of the porous structure and depends on the reaction factors below:

Cooling rate: The cooling approach includes unidirectional and multidirectional freezing. In unidirectional freezing, a directional cooling rate will enable a temperature gradient in solution, which causes ice to grow towards the applied field. The growing ice front displaces particles via diffusion and convection, accumulating them at the ice/liquid boundary layer. Arabi et al. [45] reported the effect of cooling rate influence on ice templating of gelation scaffolds; by increasing the cooling rate, the average pore size decrease, and there is no apparent difference between the morphology of pores. This is because a higher cooling rate results in smaller nuclei of ice crystals, which are, therefore, smaller in size. At a lower cooling rate, water molecules have enough time for nucleation and growth.

Concentration of solution/suspension: the concentration of particles in the suspension can affect the porous morphology and structure. The porosity value of the material can be calculated according to Equation (1).

where V_m is the volume of solution/suspension (cm³), W_m is the mass of the scaffold (g), and ρ is the density of the gelatin. Hence, high concentrations of solution/suspension will reduce the porosity of the material. The pores in lower-gelatin concentrations appeared oblate and polygonal in shape, and by increasing the concentration, the pores became more circular. Additionally, increasing the gelatin concentration resulted in a reduction in pore channel size and layer distance. This may be attributed to the increase in solution viscosity with increasing gelatin concentration, which required a higher force for gelatin molecules to be expelled by water molecules. As a result, smaller ice crystals were formed, leading to smaller pore sizes.

For electrochemistry applications, controlling the ITM is advantageous since it has a substantial impact on the electrochemical characteristics, such as surface area, porosity, and catalytic activity. For electrochemical reactions, for instance, a porous shape might offer high surface reaction active area, whereas a hierarchical structure can improve mass transport and catalytic activity. Controlling the morphology can also increase the material’s stability and toughness, making it better suited for long-term electrochemical applications. To create high-performance electrochemical devices, such as batteries, fuel cells, and sensors, morphology control of porous materials using the ITM approach is the key part.