A calibration system for an electrochemical sensor, comprising: a reference chamber containing a reference solution; a reference electrode disposed in the reference chamber and at least partially submerged in the reference solution and configured to produce a reference potential; a calibration electrode, comprising: an electrode body comprising a carbon substrate; an active surface comprising redox active functionalities for contacting the reference solution, wherein: the redox active functionalities are configured to undergo reduction/oxidation when an electrical signal is applied to the calibration electrode; and the active surface is for controlling a pH of a local environment of the reference solution proximal to the electrode, wherein either the active surface comprises a chemically modified carbon surface comprising oxygen and/or nitrogen containing functional groups; or the redox functionalities of the active surface are covalently bonded thereon; or the redox functionalities of the active surface are physically adsorbed thereon; and wherein the calibration electrode is disposed in the reference chamber and at least partially submerged in the reference solution; a voltammetric device configured to apply a voltammetric sweep between the calibration electrode and the reference electrode and receive a voltammetric response from the calibration electrode; and a processor configured to process the voltammetric response to calibrate the reference potential. a reference chamber containing a reference solution; a reference electrode disposed in the reference chamber and at least partially submerged in the reference solution and configured to produce a reference potential; a calibration electrode, comprising: an electrode body comprising a carbon substrate; an active surface comprising redox active functionalities for contacting the reference solution, wherein: the redox active functionalities are configured to undergo reduction/oxidation when an electrical signal is applied to the calibration electrode; and the active surface is for controlling a pH of a local environment of the reference solution proximal to the electrode, wherein either the active surface comprises a chemically modified carbon surface comprising oxygen and/or nitrogen containing functional groups; or the redox functionalities of the active surface are covalently bonded thereon; or the redox functionalities of the active surface are physically adsorbed thereon; and wherein the calibration electrode is disposed in the reference chamber and at least partially submerged in the reference solution; a voltammetric device configured to apply a voltammetric sweep between the calibration electrode and the reference electrode and receive a voltammetric response from the calibration electrode; and a processor configured to process the voltammetric response to calibrate the reference potential. an electrode body comprising a carbon substrate; an active surface comprising redox active functionalities for contacting the reference solution, wherein: the redox active functionalities are configured to undergo reduction/oxidation when an electrical signal is applied to the calibration electrode; and the active surface is for controlling a pH of a local environment of the reference solution proximal to the electrode, wherein either the active surface comprises a chemically modified carbon surface comprising oxygen and/or nitrogen containing functional groups; or the redox functionalities of the active surface are covalently bonded thereon; or the redox functionalities of the active surface are physically adsorbed thereon; and wherein the calibration electrode is disposed in the reference chamber and at least partially submerged in the reference solution; a voltammetric device configured to apply a voltammetric sweep between the calibration electrode and the reference electrode and receive a voltammetric response from the calibration electrode; and a processor configured to process the voltammetric response to calibrate the reference potential. the redox active functionalities are configured to undergo reduction/oxidation when an electrical signal is applied to the calibration electrode; and the active surface is for controlling a pH of a local environment of the reference solution proximal to the electrode, wherein either the active surface comprises a chemically modified carbon surface comprising oxygen and/or nitrogen containing functional groups; or the redox functionalities of the active surface are covalently bonded thereon; or the redox functionalities of the active surface are physically adsorbed thereon; and wherein the calibration electrode is disposed in the reference chamber and at least partially submerged in the reference solution; a voltammetric device configured to apply a voltammetric sweep between the calibration electrode and the reference electrode and receive a voltammetric response from the calibration electrode; and a processor configured to process the voltammetric response to calibrate the reference potential.