Tofu Waste Transformed Into Nickel Ferrite Carbon Electrode for Platinum-Free Solar Cells

Dye-sensitized solar cells have long promised a cheap, lightweight alternative to conventional silicon photovoltaics, yet one stubborn component has kept their costs uncomfortably high: the counter electrode, which is typically coated with platinum. A research team in India now reports a route to replace that precious metal entirely, using a hybrid material built from nickel ferrite nanoparticles anchored to porous carbon derived from an unlikely source—Bean Curd Stick waste, an agro-food byproduct. The work, published in the journal Ionics, presents the NiFe2O4@biocarbon composite, abbreviated NFO@BC, as a low-cost, sustainable and efficient platinum-free counter electrode for dye-sensitized solar cells.

To understand why this matters, it helps to recall how a dye-sensitized solar cell actually works. In these devices, light is absorbed by dye molecules attached to a nanostructured titanium dioxide photoanode. Excited electrons are injected into the titanium dioxide and travel through an external circuit to the counter electrode. Meanwhile, the oxidized dye is regenerated by an electrolyte, usually containing the iodide-triiodide redox couple, which itself must be regenerated at the counter electrode. The counter electrode therefore has to catalyze the reduction of triiodide back to iodide efficiently; if it does not, the whole cycle stalls and the cell’s fill factor and efficiency suffer. Platinum has been the benchmark catalyst for this reaction because of its exceptional activity and stability, but it is scarce, expensive and increasingly unattractive for mass-market deployment.

The search for platinum alternatives has become one of the most active corners of dye-sensitized solar cell research. Over the past decade, researchers have explored transition metal sulfides, selenides, nitrides, carbides and oxides as catalytic counter electrode materials, often pairing them with conductive carbon scaffolds such as graphene, carbon nanotubes or activated carbon. The logic is straightforward: the catalyst provides the electrochemical activity, while the carbon provides the electrical conductivity and surface area needed to shuttle electrons and expose active sites to the electrolyte. Ferrites—mixed metal oxides with the general formula MFe2O4—have emerged as promising candidates because they combine reasonable electrocatalytic activity with chemical stability and low cost.

The new study, led by D. Sengeni of C.K. College of Engineering and Technology in Cuddalore, Tamil Nadu, with colleagues from several Chennai institutions, takes this approach a step further by sourcing the carbon scaffold from renewable agro-food waste rather than from commercially produced activated carbon. The team converted Bean Curd Stick waste into porous biocarbon and then combined it with nickel ferrite, NiFe2O4, a spinel oxide in which nickel and iron ions occupy the crystal lattice in a way that supports electrocatalytic activity. The novel aspect of the study, according to the authors, is precisely this utilization of renewable agro-food waste as a conductive carbon matrix to fabricate a high-performance ferrite-carbon hybrid electrode.

Structural and compositional analyses confirmed the successful formation of the NFO@BC composite, while microscopic studies revealed the uniform anchoring of NiFe2O4 nanoparticles on the porous biocarbon surface. That uniformity is not merely cosmetic. In hybrid counter electrodes, the distribution of catalyst particles across the conductive scaffold determines how effectively electrons can reach active sites. If the ferrite particles cluster together, large portions of the carbon surface remain catalytically inert and the electrolyte cannot access much of the catalyst. Uniform anchoring, by contrast, means that nearly every ferrite nanoparticle is electrically connected to the carbon network and simultaneously exposed to the iodide-triiodide electrolyte, maximizing the density of accessible electrocatalytic sites.

One of the most striking quantitative results from the study comes from Brunauer-Emmett-Teller, or BET, surface area analysis, which revealed a specific surface area of 286.7 square meters per gram for the NFO@BC composite. For an electrode material, that is a substantial figure, and it has direct electrochemical consequences. A high surface area provides abundant accessible electrocatalytic sites and improved contact with the electrolyte, allowing the triiodide reduction reaction to proceed rapidly at the electrode-electrolyte interface. Porosity also matters for ion transport: the pores within the biocarbon matrix create pathways through which the electrolyte can penetrate the electrode, shortening diffusion distances and reducing the charge-transfer resistance that would otherwise limit current output.

The authors attribute the enhanced photovoltaic performance of their cells to the synergistic effect of the conductive biocarbon and the electrocatalytically active NiFe2O4. This division of labor is the central design principle of the hybrid. The biocarbon, derived from biomass, acts as a three-dimensional conductive network that collects electrons arriving from the external circuit and distributes them across the electrode. The nickel ferrite nanoparticles, dispersed across that network, serve as the catalytic workhorses where the triiodide ions are actually reduced. Neither component alone would perform as well: bare biocarbon lacks the catalytic activity of the ferrite, while bare nickel ferrite suffers from the modest electrical conductivity typical of spinel oxides. Together, they address each other’s weaknesses.

The broader context of this work is the push to commercialize dye-sensitized solar cells, which the authors identify as the motivation for developing inexpensive, effective and sustainable platinum-free counter electrodes. Dye-sensitized cells are attractive for applications where conventional panels struggle—indoor lighting, building-integrated photovoltaics, and devices that benefit from semi-transparency and flexibility. But every cost component counts. Platinum loading on a counter electrode may seem like a small fraction of a cell’s material budget, yet at the scale of gigawatt production the price of platinum becomes prohibitive, and its supply chain carries significant environmental and geopolitical burdens. Replacing it with a material synthesized from food waste and abundant iron and nickel compounds changes that calculus fundamentally.

The choice of Bean Curd Stick waste also fits into a growing body of research on biomass-derived carbons for energy devices. Biomass precursors are attractive because they are renewable, widely available and often rich in the heteroatoms that can enhance the catalytic properties of the resulting carbon. Previous work by some of the same research community has examined heteroatom doping in Bean Curd Stick-derived porous carbon for platinum-free counter electrodes, and other groups have used bamboo-derived activated carbon in similar ferrite composites. The present study extends this line of inquiry by demonstrating that the biocarbon matrix can host nickel ferrite nanoparticles uniformly, creating a composite whose texture and chemistry are both favorable for triiodide reduction.

The implications reach beyond a single laboratory result. If hybrid electrodes of this kind can be produced reliably from waste streams, dye-sensitized solar cells could move closer to the cost profile that made them famous after their invention by Brian O’Regan and Michael Grätzel in 1991. The study also illustrates a broader trend in materials science: the convergence of waste valorization and clean energy technology, where one environmental problem—food waste—is enlisted to solve another, the cost and scarcity of critical materials in renewable energy hardware. The authors conclude that NFO@BC stands out as a low-cost, sustainable and efficient platinum-free counter electrode for dye-sensitized solar cell applications, and their results suggest that the humble tofu stick, of all things, may have a role to play in the solar panels of the future.

Subject of Research: Pt-free dye-sensitized solar cell counter electrodes based on NiFe2O4 and biomass-derived biocarbon

Article Title: Development of NiFe2O4@Biocarbon hybrid counter electrode for efficient Pt-free dye-sensitized solar cells

Article References: Sengeni, D., Vinayagam, P., Karuppiah, S., Velmurugan, V., Bindhu, M., & Sevvanthi, S. (2026). Development of NiFe2O4@Biocarbon hybrid counter electrode for efficient Pt-free dye-sensitized solar cells. Ionics. https://doi.org/10.1007/s11581-026-07557-1

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07557-1

Keywords: dye-sensitized solar cells, counter electrode, NiFe2O4, biocarbon, platinum-free, Bean Curd Stick waste, nickel ferrite, biomass-derived carbon, triiodide reduction, photovoltaics, BET surface area, agro-food waste