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Abstract As the world faces an escalating energy crisis, the necessity of adopting alternative energy sources becomes increasingly evident. Despite challenges, the imperative to prioritise these eco‐friendly alternatives remains paramount in paving the way for a more sustainable and resilient future for our planet and its inhabitants. The pursuit of sustainable energy sources has brought the oxygen reduction reaction (ORR) into the spotlight as a crucial cathodic reaction in energy‐converting systems, notably fuel cells (FCs). These FCs hold tremendous promise in providing an eco‐friendly and efficient energy supply. However, the widespread implementation of FCs is hindered by their reliance on expensive and scarce noble metal catalysts, such as platinum (Pt), which pose economic and environmental challenges. Hence, this work reports the preparation, characterisation (FTIR, XPS, SEM and EDX) and application of four composites based on doped‐carbon materials (CM) and on the Wells‐Dawson POM salt K6⋅α‐[P2W12Mo6O62] ⋅ 19H2O (P2W12Mo6@MWCNT_N8, P2W12Mo6@MWCNT_N6, P2W12Mo6@MWCNT_S6, and P2W12Mo6@GF_S6) as ORR electrocatalysts in alkaline medium (pH=13). The successful doping of the carbon materials with nitrogen (N) and sulphur (S) and the incorporation of the polyoxometalate were verified through comprehensive structural characterisation. Overall, P2W12Mo6@MWCNT_N8 exhibited favourable onset potentials of 0.84 V vs. RHE, highlighting its high catalytic activity. Additionally, the catalyst showed excellent tolerance to methanol crossover, retaining 91 % of initial current, which is crucial for practical fuel cell applications. Furthermore, the P2W12Mo6@MWCNT_N8 catalyst showed commendable stability, retaining 81 % of its initial current after 36000 seconds at an operating potential of E=0.46 V vs. RHE. These encouraging results denote the significant potential of this electrocatalyst in advancing sustainable energy conversion technologies.

The oxygen reduction reaction (ORR) is a key cathodic reaction in energy-converting systems, such as fuel cells (FCs). Thus, it is of utmost importance to develop cost-effective and efficient electrocatalysts (ECs) without noble metals to substitute the Pt-based ones. This study focuses on polyoxometalate (POM)-based ECs for ORR applications. A Wells–Dawson POM salt K7 [P2W17(FeOH2)O61].·20H2O was immobilised onto graphene flakes and multiwalled carbon nanotubes doped with nitrogen, denominated as P2W17Fe@GF_N8 and P2W17Fe@MWCNT_N8. The successful preparation of the composites was proved with various characterisation techniques, including FTIR, XPS and SEM. Both materials showed good ORR performance in an alkaline medium with similar potential onset values of ~0.84 V vs. RHE and diffusion-limiting current densities of −3.9 and −3.3 mA cm−2 for P2W17Fe@MWCNT_N8 and P2W17Fe@GF_N8, respectively. Furthermore, both composites presented low Tafel slopes (48–58 mV dec−1). Chronoamperometric tests revealed that the as-prepared nanocomposites rendered a significant improvement achieving between 90 and 94% of current retention in tolerance to methanol in comparison with Pt/C, and moderate to good long-term electrochemical stability with current retentions comprised between 68 and 88%. This work reinforces the use of POMs as important electroactive species for the preparation of alternative ORR electrocatalysts, exhibiting good activity, stability and selectivity towards the ORR in the presence of methanol.

Mono-substituted vanadium-containing Dawson-type polyoxometalates having the general formula α1-[VIVW17X2O62]8− and α2-[VIVW17X2O62]8−, with X = As or P, were synthesised and subject to a comprehensive electrochemical study comprising the pH dependency. These POMs exhibit an electrocatalytic behaviour towards the oxidation of thiols (namely cysteine), rendering them interesting species for mimicking oxidative stress situations, at physiological pH values. The efficiency of the electro-oxidation was assessed with thiols of different nature, and the substrate that responded best was used to compare the electrocatalytic capabilities of the POM series. The magnetic behaviour of these POMs was also evaluated and compared to their analogues, α1- and α2-[VVW17X2O62]7− (X = As or P), at low temperatures and showed, as expected, a paramagnetic behaviour of VIV based compounds.

A novel hybrid nanocomposite, PMo11V@N-doped few layer graphene, was prepared by a one-step protocol through direct immobilization of the tetrabutylammonium salt of a vanadium-substituted phosphomolybdate (PMo11V) onto N-doped few layer graphene (N-FLG). The nanocomposite characterization by FTIR and XPS confirmed its successful synthesis. Glassy carbon modified electrodes with PMo11V and PMo11V@N-FLG showed cyclic voltammograms consistent with surface-confined redox processes attributed to Mo-centred reductions (MoVI→MoV) and a vanadium reduction (VV→VIV). Furthermore, PMo11V@N-FLG modified electrodes showed good stability and well-resolved redox peaks with high current intensities. The observed enhancement of PMo11V electrochemical properties is a consequence of a strong electronic communication between the POM and the N-doped few layer graphene. Additionally, the electro-catalytic and sensing properties towards acetaminophen (AC) and theophylline (TP) were evaluated by voltammetric techniques using a glassy carbon electrode modified with PMo11V@N-FLG. Under the conditions used, the square wave voltammetric peak current increased linearly with AC concentration in the presence of TP, but showing two linear ranges: 1.2 × 10−6 to 1.2 × 10−4 and 1.2 × 10−4 to 4.8 × 10−4 mol dm−3, with different AC sensitivity values, 0.022 A/mol dm−3 and 0.035 A/mol dm−3, respectively (detection limit, DL = 7.5 × 10−7 mol dm−3).