A soft & control, yet easily scalable reduction reaction using water soluble non-toxic biocompatible tris (hydroxy methyl) amino methane (Tris) as a mild reducing agent is explored for bulk production of partially reduced processable graphene oxide nanosheet. The excellent basic buffer action of Tris (between 7.1 and 9.0; pK(a) = 8.07 at 25 degrees C) ideally suits the reducing requirement and its ionic form acts as stabilizing agent, eliminating the requirement of additional stabilizer (polymers/surfactants) and base. The capacitance values show an increasing trend on increasing galvanostatic charge/discharge cycles up to 300 to 400 cycles and record values of similar to 461 and 373 F/g at 0.75 and 1.1 A/g current density respectively; the highest ever reported so far for partially reduced graphene oxide. More importantly, the material retains an excellent stability and durability even after 1000 cycles (>300 F/g). The cyclic voltammetric (CV) analysis shows highest capacitance value of similar to 267 F/g at 10 mV/s scan rate. The CV analysis of post charge/discharge material (after 1000 cycles) shows an interesting trend; initially capacitance value is increased on increasing scan rate (5 to 50 mV/s; highest 465 F/g value at 50 mV/s) and then slowly decreases at higher scan rate (305 F/g at 200 mV/s). (C) 2016 Elsevier Ltd. All rights reserved.