The team synthesized a carbon-coated version of the compound, NFPP/C, using a gel-combustion method, a synthesis route prized for its simplicity and scalability. The in-situ carbon coating serves a dual purpose: it improves the electronic conductivity of what is otherwise a relatively insulating phosphate framework, and it helps stabilize the electrode surface during repeated cycling. This combination is critical for polyanionic cathodes, whose inherently poor electronic transport has historically limited how fast they can be charged and discharged without sacrificing storage capacity.

What makes the new study scientifically compelling is the mechanism the researchers uncovered. When the NFPP/C electrode is first cycled in an aqueous lithium nitrate electrolyte, it does not initially behave as a lithium-ion host. Instead, the initial cycles trigger a gradual ion-exchange process in which lithium ions from the electrolyte replace sodium ions within the polyanionic structure. The team confirmed this structural transformation using ex-situ X-ray diffraction, which revealed the evolving crystalline phases as the exchange progressed. Only after this conditioning period does the electrode settle into a stable redox regime corresponding to genuine lithium-ion insertion and de-insertion from the framework.

Once that stabilization was achieved, the performance was striking. The electrode delivered a highly stable specific capacity of approximately 117 milliampere-hours per gram at a scan rate of 20 millivolts per second, a figure close to the theoretical capacity predicted for the compound. For context, capacities measured at such high scan rates reflect the material’s ability to operate under fast-charging conditions, so reaching near-theoretical values at speed is a meaningful benchmark rather than a laboratory curiosity achievable only at impractically slow rates.

The comparison with sodium storage revealed an intriguing split personality in the material. When tested for sodium-ion storage in an analogous aqueous sodium nitrate electrolyte, the same composite delivered a comparable capacity of 122 milliampere-hours per gram at the 20 millivolts per second scan rate. But when the researchers varied the scan rate, the two ions behaved differently in ways that illuminate the underlying physics. At low scan rates of 1 millivolt per second, lithium storage outperformed sodium storage, delivering 128 versus 118 milliampere-hours per gram. At high rates of 50 millivolts per second, the ranking flipped, with sodium pulling ahead at 97 versus 79 milliampere-hours per gram.

The explanation lies in the balance between two competing factors: the intrinsic thermodynamics of ion insertion and the kinetics of ion transport through the electrolyte and the electrode. Lithium ions are smaller and carry a higher charge density, which favors their insertion into the framework when time is not a constraint. Sodium ions, by contrast, are larger but benefit from the openness of NFPP’s three-dimensional polyanionic framework, and at high scan rates the ionic conductivity of the electrolyte becomes the determining factor, allowing the more diffusively mobile sodium ions to win. Chronopotentiometry measurements, which track the voltage response of the electrode under constant current, showed the same trend, reinforcing the reliability of the observation across two independent electrochemical techniques.

Long-term cycling tests over more than 100 cycles in both lithium nitrate and sodium nitrate solutions added a further layer of nuance. Capacity retention proved better in the lithium nitrate electrolyte, suggesting that the lithium-conditioned structure is somewhat more robust under repeated insertion and extraction. However, the cycling data also indicated that both lithium and sodium ions are co-inserted during operation rather than acting in strict isolation. This co-insertion behavior means the electrode does not behave as a pure single-ion intercalation host in practice, a detail that will matter for engineers designing cells around this chemistry but which also underscores the flexibility that makes the material attractive.

The broader significance of the work lies in what it says about the dual Na-Li functionality of NFPP/C in aqueous systems. A cathode that can operate with either ion, or with a mixture of both, gives battery designers an unusual degree of freedom. Water-based electrolytes are inherently non-flammable, inexpensive and tolerant of manufacturing imperfections that would be dangerous in organic-solvent cells, and pairing them with an earth-abundant iron phosphate cathode pushes the chemistry toward the low-cost, safe, sustainable end of the battery spectrum that grid storage and stationary applications demand.

The result also connects to a vigorous research frontier. Polyanionic cathodes have emerged as leading candidates for next-generation sodium batteries precisely because their rigid frameworks can be tuned through phosphate and pyrophosphate building blocks to stabilize multiple redox couples, and iron-based compositions avoid the cobalt and nickel supply chains that plague conventional cathodes. The new study extends that logic by showing that the same framework, already proven in commercial sodium cells, can be repurposed for lithium chemistry in water, effectively letting one material serve two distinct battery ecosystems.

Challenges remain before such aqueous dual-ion chemistry reaches commercial hardware. The ion-exchange conditioning period must be understood and controlled during cell manufacturing, the co-insertion of mixed ions will need to be managed to guarantee predictable long-term performance, and the modest capacities of polyanionic materials still trail the best organic-electrolyte cathodes in energy density. Yet the study provides a clear proof of concept: a commercially established sodium cathode, synthesized by a simple combustion route, can approach its theoretical capacity while storing lithium ions in water. For a field racing to make batteries safer, cheaper and more sustainable, that is a result worth watching closely.

Subject of Research: Lithium and sodium ion storage in Na4Fe3(PO4)2(P2O7)/C cathodes in aqueous electrolytes

Article Title: Electrochemical behaviour of Na4Fe3(PO4)2(P2O7)/C in an aqueous Li+ electrolyte

Article References: Gezović-Miljanić, A., Mišurović, J., Grudić, V., Dominko, R., & Vujković, M. (2026). Electrochemical behaviour of Na4Fe3(PO4)2(P2O7)/C in an aqueous Li+ electrolyte. Ionics. https://doi.org/10.1007/s11581-026-07475-2

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07475-2

Keywords: aqueous batteries, NFPP, cathode material, sodium-ion battery, lithium-ion storage, polyanionic cathode, gel-combustion synthesis, ion exchange, iron phosphate, capacity retention, mixed ion insertion, energy storage

The research team, led by Sachin Naik and Michelle Jones, drew on a curated collection of 1,044 rhizobacterial isolates originally recovered from ornamental greenhouse crops grown in peat-based substrates. Rather than relying on the traditional tricalcium phosphate assays that dominate the phosphate-solubilizing bacteria literature, the team targeted iron phosphate directly, reasoning that the calcium-focused screens used in most prior studies may miss the strains most relevant to soilless production. Peat substrates contain significant intrinsic iron, much of it bound to organic matter, and under the mildly acidic to near-neutral conditions typical of greenhouse containers, phosphorus is progressively sequestered into stable iron phosphate precipitates that resist conventional fertilizer corrections.

To find bacteria that could liberate this trapped nutrient, the researchers deployed a high-throughput malachite green colorimetric assay. Each isolate was grown in triplicate in minimal medium containing iron phosphate dihydrate as the sole phosphorus source, and after four days of incubation the soluble phosphorus released into the culture supernatant was quantified spectrophotometrically. The results revealed a strikingly stratified microbial landscape: nearly 70 percent of the isolates showed minimal solubilization below 8 percent, about 28 percent displayed moderate activity, and only 24 isolates, a mere 2.3 percent of the collection, exceeded the 25 percent threshold set for high performers. Notably, Bacillus velezensis, the phosphate-solubilizing strain included as a commercial reference from the biostimulant Lalrise Vita, showed almost no activity against iron phosphate, solubilizing less than 3 percent.

Whole-genome sequencing of the top performers revealed a taxonomically diverse guild dominated by the genera Pantoea, Bacillus, Priestia, Paenibacillus, Pseudomonas, and Stenotrophomonas. Average nucleotide identity analysis confirmed species-level assignments for most strains, and the isolates proved remarkably cosmopolitan in origin, having been recovered from zinnia, vinca, petunia, geranium, and coleus. This broad host distribution suggests these bacteria are not tightly host-specific but instead occupy shared rhizosphere niches across taxonomically diverse plant families, a property that could make them useful in the mixed plantings and crop rotations common in commercial greenhouse operations.

The critical question, of course, was whether laboratory solubilization would translate into real plant benefit. Twenty-seven candidate strains were tested in a high-throughput greenhouse experiment using French marigold ‘Durango Yellow’ grown in peat-perlite substrate adjusted to pH 7.0, a deliberately severe phosphorus-limiting condition. After seedling establishment, insoluble iron phosphate served as the sole phosphorus source, and bacterial treatments were applied as weekly substrate drenches for four weeks. A laser-based digital phenotyping platform measured plant biomass, leaf area, and spectral reflectance indices that track chlorophyll content, canopy greenness, and senescence. Five strains emerged as clear winners: Pantoea communis C3A8, Pantoea formicae C8D10, Pseudomonas sp. C6E7, Pseudomonas sp. C9D1, and Priestia megaterium C3F10.

Intriguingly, two of those five, strains C3F10 and C9D1, had shown only about 3 percent solubilization in the in vitro assay, yet they ranked among the top performers in the greenhouse screen. This disconnect between biochemical activity in a flask and plant growth promotion in a pot carries an important lesson for biofertilizer development: in vitro solubilization percentage alone does not reliably predict in planta performance. The researchers deliberately included low and mid-range solubilizers in their greenhouse trials to test this very question, and the answer was unambiguous. Success in the rhizosphere depends on far more than raw solubilizing chemistry, encompassing colonization ability, stress tolerance, and the competitive exploitation of root-derived carbon.

A second, more rigorous validation experiment with 30 replicate blocks confirmed the greenhouse results at pH 6.5. Pantoea communis strain C3A8 delivered the strongest overall response, significantly increasing shoot digital biomass and 3D leaf area while boosting the green leaf index and shifting canopy color composition toward healthier green hues. Most tellingly, plants inoculated with C3A8 accumulated significantly more phosphorus in their shoot tissue than controls. Because iron phosphate was the only phosphorus supplied during the treatment period, this tissue analysis provides direct evidence that the bacterium released plant-available phosphorus from the insoluble iron phosphate pool. The authors believe this is the first report of phosphate solubilization ability in P. communis, expanding the known functional diversity of a genus previously represented mainly by P. agglomerans in this literature.

The genomic analysis explains why these strains differ so markedly in performance. Pantoea communis C3A8 and Pantoea formicae C8D10 each carry three copies of the gcd gene, which encodes glucose dehydrogenase, the central enzyme in gluconic acid-mediated inorganic phosphate solubilization, along with the pqqF and pqqL genes needed to synthesize its pyrroloquinoline quinone cofactor. Both also harbor extensive arsenals of phosphatase genes for mineralizing organic phosphorus, complete phosphate transport systems, and hundreds of genes for iron acquisition and root colonization. The Pseudomonas strains took a different genomic route, pairing single gcd copies with multiple pqqL copies, three copies of phoD and ppx in C6E7, and elevated counts of nitrogen acquisition and volatile synthesis genes. Priestia megaterium C3F10, remarkably, lacks gcd entirely and may instead rely on intracellular polyphosphate accumulation and controlled release, driven by five copies of the phosphoenolpyruvate synthase gene and multiple phoR regulatory copies.

Rhizosphere competence genes added another layer of ecological insight. The Pantoea strains carry multiple gene clusters for trehalose and mannitol catabolism, pathways linked to osmoprotection and persistence under the fluctuating moisture conditions of container substrates, while C3A8 uniquely encodes an inositol catabolic cluster, a trait shown in other bacteria to be essential for rhizosphere colonization. Priestia megaterium C3F10 carries gene clusters for sucrose and levan metabolism, which in other systems support biofilm formation and root surface attachment, along with the 3-oxoadipate pathway for degrading aromatic compounds derived from lignin and phenolic root exudates. The authors are careful to note that these genomic signatures generate hypotheses about mechanism rather than demonstrated links, and that direct substrate-level measurements of water-extractable phosphorus and rhizosphere enzyme activity will be needed to confirm which solubilization pathways operate in situ.

The practical implications extend well beyond ornamental horticulture. Greenhouse production depends almost entirely on fertigation, and the limited substrate volume and low cation exchange capacity of soilless containers routinely drive fertilizer runoff, phosphorus leaching, and environmental contamination. Growers frequently over-apply phosphorus to compensate for its rapid immobilization, a practice that wastes resources, disrupts micronutrient balance, and can even induce iron deficiency in crops. The five validated strains, with their complementary mechanisms spanning gluconic acid-mediated dissolution, organic phosphorus mineralization, nitrogen acquisition, and polyphosphate dynamics, suggest that microbial consortia could deliver synergistic benefits exceeding those of any single inoculant. If follow-up work confirms performance across diverse ornamental species and substrate types, these iron phosphate solubilizers could form the basis of biofertilizer formulations that let growers cut synthetic phosphorus inputs while maintaining crop quality, turning a stubborn chemistry problem into a biological opportunity.

Subject of Research: Iron phosphate solubilizing bacteria for sustainable phosphorus management in soilless greenhouse crop production

Article Title: High-throughput screening and genomic characterization of iron phosphate solubilizing bacteria for sustainable greenhouse production

Article References: Naik, S., Quijia-Pillajo, J., Chapin, L. J., & Jones, M. L. (2026). High-throughput screening and genomic characterization of iron phosphate solubilizing bacteria for sustainable greenhouse production. Plant and Soil. https://doi.org/10.1007/s11104-026-09134-x

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09134-x

Keywords: phosphate solubilizing bacteria, iron phosphate, greenhouse production, soilless substrate, plant growth promoting rhizobacteria, Pantoea communis, Pseudomonas, Priestia megaterium, whole genome sequencing, phosphorus availability, biofertilizer, controlled environment agriculture