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• The loading of CNT into acid-treated carbon papers enhances the 2e-transfer process. • The Faradaic efficiency for H 2 O 2 production using CNT/a-CP cathodes is ˜100. • The Faradaic efficiency for As(III) oxidation using h-TNR photoanodes is >80%. • The h-TNR and CNT/a-CP pair drives the As(III) oxidation and H 2 O 2 production. We present an off-grid, standalone electrocatalytic H 2 O 2 production reaction (HPR) using carbon nanotubes (CNT) wired to hydrogen-treated TiO 2 nanorod (h-TNR) arrays catalyzing the oxidation of As(III) to As(V) under simulated solar light (AM 1.5; 100 mW cm−2). Loading CNT onto acid-treated carbon paper (a-CP) significantly enhances the catalytic 2-electron transfer to O 2 , leading to a Faradaic efficiency (FE) of ∼100% for the HPR. To drive the HPR, the 2-electron oxidation of toxic As(III) to less toxic As(V) that accompanies the production of the proton/electron couples is achieved at an FE of >80% using the h-TNR arrays. The high FEs of the anodic and cathodic reactions are maintained over 10 h when a direct-current voltage of 0.7 V is applied to the h-TNR photoanode and CNT/a-CP cathode pair. The coupling of a mono-Si photovoltaic array that is one-tenth the size of h-TNR photoanode to the pair of h-TNR and CNT/a-CP successfully drives the standalone operation of both reactions at the high FEs (>90%). The surface characterization of the as-synthesized materials and the reaction mechanism are discussed in detail. [ABSTRACT FROM AUTHOR]