Fluorescence-based imagining techniques represent one of the central routes for achieving the goal of spatiotemporal visualization of electrochemical reactions . Few reports are available on the sensing of electrochemical reactions using a fluorophore that is responsive to any one the reactions products . This, however, requires the application of highly specific fluorophores for the specific product, and thus cannot be extended universally to different electrochemical processes . Additionally, most of the works in literature report on the fluorescence sensing of the electrochemical products, rather than the in-situ imaging or visualization of any electrochemical reactions . Furthermore, it is very important to provide the quantitative inoperando visualization of the electrochemical reactions, which is usually missing in existing literature investigations . Acid/base (or pH) fluorescent probes can be one of the best candidates for visualization purposes, as most of the electrochemical reaction involve the oxidation or reduction of specific moieties which cause a concomitant decrease or increase in the environment pH, at one or both of the electrodes simultaneously . These change in pH can be monitored using an acid/base (pH)-sensitive fluorescent probes for monitoring the insitu progress of any electrochemical reaction. The pH-based visualization of electrochemical reactions can be universally applied to various electrochemical processes, however presently suffers majorly due to limited range of suitable fluorescent probes displaying chemical and electrochemical stability in the voltage window of interest, the use of multiple fluorescent dyes for specific tasks and voltage range of interest, the lack of a suitable visualization approach, etc. which overall make the spatiotemporal visualization process very complex. Recently, Roberts et al. used a combination of dyes to monitor a electrocoagulation process by observing the pH changes in the range of 1.5 to 8.5. To address the issues, we have explored HPTS (8-hydroxypyrene-1,3,6-trisulfonicacid) as a fluorescent probe, with a neutral pKa of 7.4 in the ground state. HPTS is a well-known photoacid molecular species, displaying a sharp transition from is pKa of 7.4 in the ground state, being a weak acid, to a pKa of ~0.5 in its photo-excited state, making it a strong acid upon excitation. The exceptional properties of the HPTS molecule allow it to monitor any minute changes from neutrality, to acidic or basic conditions, thus allowing the use of a single fluorescent probe. Furthermore, the optical fluorescence properties of the molecule allow the ratiometric sensing of the acid/basic transitions, and thus can be used for the reliable qualitative and quantitative analysis of any small changes in the environment. In the past few decades, electrocatalytic water splitting for hydrogen gas production was established as a basis for sustainable development, and has led to significant progress in terms of efficiency and achievably low overpotentials under alkaline/acidic conditions . Corrosive environment, use of additives and expensive separators have very recently shifted the research attention to the realization of neutral water splitting . However, it is at an initial state and necessitates innovative characterization tools for better understanding of the electrocatalytic water splitting under unbuffered neutral conditions . In this work, for the first time, direct spatiotemporal dynamic in-situ optical visualization of on-catalyst water splitting processes is performed under neutral condition by exploiting the exceptional fluorescent properties of the HPTS probe . Under neutral conditions, the oxidation and reduction of water (for production of oxygen and hydrogen) at anode and cathode, respectively, leads to the formation of acidic and basic environments around the electrodes at neutral conditions . This associated formation of acid and base 'fronts' leads to a decrease and increase in the pH, respectively, which can be optically visualized directly by the opto-electrochemical cell developed in this study . Recently, Obata et al. attempted bulk in-situ imaging of the water splitting process under neutral conditions, and successfully observed the concomitant formation of acid and base and its associated pH changes. However, the work involved the use of a fluorescent strip in between the two electrodes, which lead to limitations of minimum uncontrollable contact nature with the electrodes, resulting in contact aberrations, non-microscopic imaging capabilities with low-resolution and limited dimensional imaging, completely lacking 3D optical information of environmental chemical changes. Considering this broad research gap, the quest for a fluorescent probe is realized which can directly be added to the electrolyte medium for in-operando visualization of water splitting reactions. Thus, an optoelectrochemical cell, using HPTS as a fluorescent probe, was developed which demonstrates the following unprecedented advantages: (i) universal indicator for acid and base (pH) environment changes, (ii) direct homogeneous addition into the cell electrolyte, (iii) 3D spatial imaging capabilities, (iv) ratiometric fluorescence analysis and (v) easy qualitative and quantitative analysis in a single system. As a result, the opto-electrochemical cell developed in this work is successfully able to quantitatively visualize the spatiotemporal development of acidic and basic fronts at the anode and cathode surfaces during the water splitting process reactions. Furthermore, the ability of the opto-electrochemical cell to spatially visualize in-situ water splitting reactions was practically applied to unveil further key insights on the efficiency of unbuffered neutral water splitting. Specifically, the possibility of 'self-neutralization' via optimizing the distance gap between the electrodes, as well as the effect of applying different electrolyte "flow" conditions, at different flow rates, on the water splitting process were here investigated by in-situ opto-electrochemical imaging platform, under static and under-flow electrolyte conditions, leading to the experimental discovery of key new insights that allow further enhancing the water splitting process under neutral conditions. Additionally, this approach was here universally applied for the spatiotemporal monitoring of chemical byproducts other than pH changes, such as the formation of hypochlorite and chlorine species using a specific fluorophore, concomitantly produced during the sea water splitting process under neutral conditions. This shows the universal nature of our novel experimental paradigm that can be extended to any electrochemical reaction per se.